Okamikurainya

Flu is an abbreviation for the literal Influenza Virus, a real virus that exists, while a Cold is a colloquial term for any number of upper respiratory tract infections. Though you're right, folk do use Flu incorrectly a lot of the time.
 
For gameplay, having a catch all treatment for a disease that would be more common than others and can be caught ambiently lowers the amount of micro management. You can still treat individual symptoms, as I have stated above. I disagree with you here.
 
That is in a world where a majority of people are not directly interacting with wildlife, like they would be forced to in the post-zombie-apocalypse. Rabies cases are mostly when a rabid animal happens to wander into civilization and bites someone or their pet which then may bite a person. The amount of incidences will go way up when large portions of survivors move into the wilderness.
I live in a rural town and we have a case of Rabies in the stray animal population at least once or twice a year. This is Africa though, so there's that.
That said, Tetanus is a great idea for an additional disease! Thanks!
Just realized that Tetanus wouldn't be functionally different in the game's meta from the Common Infection, so I just left it at that.

Added Vaccines in the Medications and added Syringe in the Items. :3

Right now, the way disease is handled contrasts starkly with the overall complexity of the game...

My suggestion is to remove the ambiguity and turn certain Moodles into Symptoms, rather than have them as the disease themselves.
 
Symptoms:
Congestion:
Congestion replaces the Cold Moodle, becoming a symptom. It functions near identically, giving the player a chance to sneeze loudly, attracting zombies. Can be aided with an equipped tissue and treated with Antihistamines.
"Runny Nose"
"The sniffles"
"Congested"
"Severe Congestion" Fever:
Fever replaces the current Sick Moodle, becoming a symptom. Each stage will increase your character's temperature by a certain amount and will cause damage on its' highest level while also lowering healing, strength and increasing the rate at which a player gets sleepy. Can be treated with Antipyretics unless it is a symptom of Zombification. Equipping a Cold Pack that has been cooled in a freezer or a bag of Frozen Peas can also help.
"Bit of a Temperature"
"Temperature"
"Severe Temperature"
"Terminal Fever" Nausea:
Nausea is the other half of the current Sick Moodle becoming a symptom in its' own right. It lowers healing, strength and speed. It can be treated with Antiemetics.
"Bit Sick"
"Sick"
"Really Sick"
"Severe Nausea" Sore Throat:
A Sore Throat is similar to Congestion, but may cause pain when eating with an increasing chance to loudly cough which may attract nearby zombies. Can be treated with Cough Syrup.
"Scratchy Throat"
"Painful Throat"
"Rough Cough"
"Severe Coughing" Shivers:
Shivering which will lower the accuracy of the player. Can be relieved with Painkillers.
"A bit Shaky"
"Shaky"
"Shivering"
"Severe Shivering"  
While those are direct symptoms, other Moodles such as Pain would also be symptoms, directly or indirectly.

Medications:
Painkillers:
Relieves Pain and Shivers. Can cause Nausea if abused. Beta Blockers:
Relieves Panic. Antidepressants:
Relieves Sadness. Can cause Anger if abused. Sleeping Tablets:
Helps you sleep. Can cause Nausea or loss of Health if abused or taken while Drunk. Vitamins:
These should boost healing and help you recover some Immunity. Antibiotics:
Speeds up healing of Colds, Pneumonia, Infection and Stomach Flu. Can cause Nausea if abused. Caffeine Pills:
Relieves Sleepiness. Can cause Shivers if abused. Antihistamines:
Relieves Congestion. Can cause Sleepiness if abused. Antipyretics:
Relieves a traditional Fever. Can cause Nausea if abused. Antiemetics:
Relieves Nausea. Cough Syrup:
Relieves a Sore Throat, may also make you Drunk if taken in large quantities. Flu Vaccine Vial:
A vial containing a Vaccine for the Flu Virus. Can be added to a syringe so that you can administer a Flu Shot. Each Vial can fill a Syringe 4 times. Taking a Flu Shot will cause the Severity of Flu to begin to decline and will provide you with a month of immunity to the Flu Virus. Common Infection Vaccine Vial:
A vial containing a Vaccine for the Infection. Can be added to a syringe so that you can administer a Common Infection Shot. Each Vial can fill a Syringe 4 times. Taking a Common Infection Shot will cause the Severity of a Common Infection to decline and will provide you with a month of immunity to the Common Infection. Rabies Vaccine:
A vial containing a Vaccine for the Rabies Virus. Can be added to a syringe so that you can administer a Rabies Shot. Each Vial Can fill a Syringe 4 times. Taking a Common Infection Shot will cure Rabies, provided you take it prior to the manifestation of symptoms, and will provide you with a month of immunity to the Rabies Virus.  
There are a few others I'd like such as Morphine and so on that would have a chance to cause addiction, but the ones I've added are more to expand on what is present, rather than add too much new.
 
Items:
Pill Dispenser:
A container with random pills inside. Water bottle with Dissolved Painkiller:
As the name suggests. The Player can dissolve up to 4 units of Painkillers into a Water Bottle, allowing for Painkiller use to be stretched out, if a bit weakened. Surgical Mask:
Surgical Masks (along with gasmasks) provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, as long as they are at least 50% clean with no damage. Hazmat Gear:
A full set of Hazmat Gear will provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, so long as they are undamaged. Syringe:
A medical syringe used for injecting yourself with a Vaccine. Maybe also for Addictive Drugs. Empty Vial:
Garbage item left over when adding a Vaccine to a Syringe. Can hold water.  
Traits:
Strong Immune System:
Chance of catching a disease is halved. Can go well with Iron Gut and Outdoorsman for a Robust Genetics build. Weak Immune System:
Replaces Prone To Illness. Chance of catching a disease is doubled, more likely for a wound to be infected and faster Zombification. Iron Gut:
Chance of catching Stomach Flu from food or water is halved. Weak Stomach:
Chance of catching Stomach Flu doubled. Outdoorsman:
Being wet does not weaken your Immune System. Immune to Hayfever. Allergy Prone:
Very prone to Hayfever. Hayfever gained this way bypasses Immune System Variable with there always being a 10% chance of contracting Hayfever when moving through thick Vegetation in off seasons and a 25% chance in Spring. Resilient:
Less likely for wounds to become infected and slows Zombification. Asthmatic:
40% increase in running endurance loss, 30% increase in swing endurance lost and a chance to loudly cough when Exerted. Hypochondriac:
May develop infection symptoms without being infected. Easily Amused:
Slower rate of boredom and unhappiness. Depression:
Becomes bored faster and gradually becomes sadder with time.  
The Immune System:
The Immune System, or simply just the Immunity variable, determines the chance of becoming ill.
At 0%, you are fully healthy and won't get sick.
But any activity while Sick, Dirty, Bloody, Wet, Sleepy, Exerted, Sad, Injured or Hungry will cause it to gradually rise. At 1%, you have a 1% chance of catching a disease and so on.
Sleeping will help you recover your Immunity most of the time, however putting yourself to sleep with Sleeping Pills or Alcohol will prevent this recovery. Being well fed will also help you recover.
This variable is invisible to the player, as it is to a real person.
 
Severity:
When catching a disease, it will gradually rise in severity, before reaching a peak and lowering again in severity until the disease is gone. During this time, all you can do is treat symptoms and rest until you are better. There are 4 levels of Severity, based on when the disease's variable is at 1%-25%, 26%-50%, 51%-75% and 76%-100%.
Certain diseases, when treated with certain medications and the disease's variable reaches 0% will then be cured.
 
Nutrients:
There are many nutrients which a player will gain with a balanced diet. Lacking certain nutrients in your diet for too long will result in a Nutritional Disease. Nutritional Diseases bypass the immune system.
Calories:
Calories are the main weight determining nutrient. This value must be balanced with hunger consistently, or else obesity or anorexia may sneak up on the player.
Maximum: 3700
Minimum: -2200 Carbohydrates:
Carbohydrates are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Carbohydrates, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Lipids:
Lipids, previously called fats, are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Lipids, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Proteins:
Proteins are a determining factor in the increase and decrease of the Player's strength stat. Without the necessary proteins, the player will not be able to level up their strength. If a player consumes more than 400 Protein units, they will increase their strength in the same way as in the same manner as B40/B41. If the player consumes more than 700 Protein units, they will gain a 1.5 multiplier for strength increase. If a player's protein units falls below -250, they will start to lose strength, and reaching the minimum Protein units of -500 will result in the loss of strength with a multiplier of 2.
Maximum: 1000
Minimum: -500 Salts:
Salts can alter the rate at which a player becomes thirsty. This value is ignored unless the player has consumed more than 400 or 700 Salts resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Sugars:
Sugars are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Sugars, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Vitamins:
Vitamins are essential for keeping your Immune System strong. So long as the player consumes more than 400 Vitamins, their Immunity will recover as per normal while resting or sleeping. If the Sugar unit falls below 0, their Immunity will no longer recover.
Maximum: 500
Minimum: -500  
Diseases:
Diseases are visible in the Health tab when you have a certain level of First-Aid, but otherwise you'll have to guess by symptoms and circumstances.
Flu:
Sometimes, Zombies, Pigs (when added) or Chickens (when added) will spawn as infected with the Flu Virus. Being within 5 tiles from an infected zombie, the infected Zombie's corpse, an infected Player, an infected Player's corpse, an infected Pig or Chicken and an infected Pig or Chicken's corpse will make you vulnerable to catching the flu. Pigs and Chickens will also be at risk of catching it.
Symptoms are Congestion, Fever, Pain and a Sore Throat.
After catching Flu, there is a cooldown time before you can catch it again of around a month.
Severity 1:
The Flu is Asymptomatic at this severity, increasing the likelihood that you will spread it to other players unwittingly.
Severity 2:
Level 2 symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms, risk of death without treatment.
  Cold:
A cold is an ambient bacterial infection that can be caught when being wet, hot, cold or tired. Similar to Flu but far less severe but also far quicker to show symptoms.
Symptoms are Congestion, Fever and a Sore Throat.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Congestion and Sore Throat, no Fever.
Severity 2:
Level 2 Congestion and Sore Throat, no Fever.
Severity 3:
Level 3 Congestion and Sore Throat, Level 1 Fever.
Severity 4:
Level 4 Congestion and Sore Throat, Level 2 Fever.
  Pneumonia:
An ambient infection of the lungs that can be caught while Hypothermic. Similar to a Cold but far more severe.
Symptoms are Fever, Sore Throat and Shivers.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Sore Throat and Shivers, no Fever.
Severity  2:
Level 2 Sore Throat, Shivers and Fever.
Severity 3:
Level 3 Sore Throat, Shivers and Fever.
Severity 4
Level 4 Sore Throat, Shivers and Fever. Risk of death without treatment.
  Hayfever:
Can be caught by moving through dense vegetation during Spring.
Symptoms are Congestion and a Sore Throat.
Can be treated directly with Antihistamines.
Severity 1:
Level 1 Congestion, no sore throat.
Severity 2:
Level 2 Congestion, no Sore Throat.
Severity 3:
Level 3 Congestion, Level 1 Sore Throat.
Severity 4:
Level 4 Congestion, Level 2 Sore Throat.
  Stomach Flu:
An infection of the stomach lining, can be caught by eating uncooked or rotten food as well as drinking tainted water.
Symptoms are Nausea, Fever and Shivers.
Can be treated directly with Antibiotics.
Severity 1:
Level 1 Nausea, no Fever or Shivers.
Severity 2:
Level 2 Nausea, no Fever or Shivers.
Severity 3:
Level 3 Nausea, Fever and Shivers.
Severity 4:
Level 4 Nausea, Fever and Shivers. Risk of Death if untreated.
  Bleach Poisoning:
Bleach poisoning is a fast onset and fatal illness caused by directly drinking Bleach. It is always Severity 4.
Symptoms are Sore Throat, Pain, Anxiety, Shivers and gradual loss of Health.
Severity 4:
Level 4 Symptoms. Death is certain.
  Food Poisoning:
Food Poisoning is similar to Botulism but is caught by eating Poison Berries, Poison Mushrooms or food poisoned with Bleach.
Symptoms are Nausea, Sore Throat, Pain, Shivers and gradual loss of Health.
Severity 1:
Level 1 Nausea and Sore Throat, no others.
Severity 2:
Level 2 Nausea and Sore Throat, Level 1 Pain and Shivers. No loss of Health.
Severity 3:
Level 3 Nausea and Sore Throat, Level 2 Pain and Shivers. No loss of Health.
Severity 4:
Level 4 Nausea, Sore Throat, Pain, Shivers and a gradual Loss of Health. Can be fatal even with treatment if health already low.
  Rabies:
Caught by being Bitten by an infected animal. It is always Fatal if not treated with a Rabies Vaccine prior to Severity 2.
Symptoms are Anger, Stress, Weakness, Sore Throat, Agoraphobia, Pain when Drinking or Eating and Gradual Loss of Health.
Severity 1:
No symptoms.
Severity 2:
Level 2 Symptoms, but no loss of Health.
Severity 3:
Level 3 Symptoms, but no loss of Health.
Severity 4:
Level 4 symptoms and gradual loss of Health. Death is certain.
  Infection:
Caught by not properly treating a wound or spending a lot of time around corpses while your immune system is compromised.
Symptoms are Nausea, Pain, Shivers and Fever. If playing as a Hypochondriac, the symptoms are identical to Zombification if contracted from a Zombie Scratch instead but not always fatal.
Can be directly treated with Antibiotics or applying a sterilizing agent to the infected wound.
Severity 1:
Level 1 Nausea, no other symptoms.
Severity 2:
Level 2 Symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms. Can be fatal if left untreated.
  Scurvy:
Scurvy is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Vitamin intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Scurvy. Taking in the proper amount of Vitamins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Shivers, Pain and gradual loss of Health.
Can be directly treated with food rich in Vitamins or Vitamins medication.
Severity 1:
Level 1 Shivers and Pain, no loss of Health.
Severity 2:
Level 2 Shivers and Pain, no loss of Health.
Severity 3:
Level 3 Shivers and Pain, no loss of Health.
Severity 4:
Level 4 Shivers and Pain and the gradual loss of Health. Can be fatal if left untreated.
  Anemia:
Anemia is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Protein intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Anemia. Taking in the proper amount of Proteins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sleepiness, Weakness, Decreased Spatial Awareness, lowered item transfer rate and the gradual loss of Health.
Can be directly treated with food rich in Proteins.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Thyroditis:
Thyroditis is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Salt intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Thyroditis. Taking in the proper amount of Saltss will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sore Throat, Shivers and the gradual loss of Health.
Can be directly treated with food rich in Salts.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Zombification:
Caught by being Bitten or Scratched by a Zombie. It bypasses Immune system, with Bites always resulting in being infected and a 25% chance of being infected by a Scratch.
Symptoms are Stress, Sadness, Nausea, Untreatable Fever and the eventual death and rising as a Zombie.
Severity 1:
Level 1 Stress, no other Symptoms.
Severity 2:
Level 2 Stress, Level 1 Sadness, no other Symptoms.
Severity 3:
Level 3 Stress, Nausea, Sadness and Fever.
Severity 4:
Level 4 Stress, Nausea, Sadness and Fever. Death is certain.  
Abilities:
Players with high First-Aid or medical related Occupations/Traits will be able to deduce illnesses and administer medication directly to another Player, so Doctors and Nurses will have even more use in Multiplayer.
 
And that's that! Did I miss anything? What did y'all think?

Just a small little addition that I think could work well for group survival, as well as just some quality of life goodness...

The ability to dish up up certain foods, such as stirfry, onto plates in a similar manner as adding soup and such to bowls.
Then once added in, there would be a slot opened up similar to adding spices which will allow certain utensils to be added which will increase the happiness gained from the meal. Soup will allow for spoons, whilst stirfry and such on a plate or bowl could have a knife and fork added to it. On consumption, the utensils will be returned to the player, perhaps dirty. This will increase the usefulness of the utensils and give you a reason to keep them around, rather than just being disposable last resort weapons.
Eating without utensils while you're covered with zombie blood and dirt could increase the risk of food poisoning by a bit.
 
What y'all think?

Right now, the way disease is handled contrasts starkly with the overall complexity of the game...

My suggestion is to remove the ambiguity and turn certain Moodles into Symptoms, rather than have them as the disease themselves.
 
Symptoms:
Congestion:
Congestion replaces the Cold Moodle, becoming a symptom. It functions near identically, giving the player a chance to sneeze loudly, attracting zombies. Can be aided with an equipped tissue and treated with Antihistamines.
"Runny Nose"
"The sniffles"
"Congested"
"Severe Congestion" Fever:
Fever replaces the current Sick Moodle, becoming a symptom. Each stage will increase your character's temperature by a certain amount and will cause damage on its' highest level while also lowering healing, strength and increasing the rate at which a player gets sleepy. Can be treated with Antipyretics unless it is a symptom of Zombification. Equipping a Cold Pack that has been cooled in a freezer or a bag of Frozen Peas can also help.
"Bit of a Temperature"
"Temperature"
"Severe Temperature"
"Terminal Fever" Nausea:
Nausea is the other half of the current Sick Moodle becoming a symptom in its' own right. It lowers healing, strength and speed. It can be treated with Antiemetics.
"Bit Sick"
"Sick"
"Really Sick"
"Severe Nausea" Sore Throat:
A Sore Throat is similar to Congestion, but may cause pain when eating with an increasing chance to loudly cough which may attract nearby zombies. Can be treated with Cough Syrup.
"Scratchy Throat"
"Painful Throat"
"Rough Cough"
"Severe Coughing" Shivers:
Shivering which will lower the accuracy of the player. Can be relieved with Painkillers.
"A bit Shaky"
"Shaky"
"Shivering"
"Severe Shivering"  
While those are direct symptoms, other Moodles such as Pain would also be symptoms, directly or indirectly.

Medications:
Painkillers:
Relieves Pain and Shivers. Can cause Nausea if abused. Beta Blockers:
Relieves Panic. Antidepressants:
Relieves Sadness. Can cause Anger if abused. Sleeping Tablets:
Helps you sleep. Can cause Nausea or loss of Health if abused or taken while Drunk. Vitamins:
These should boost healing and help you recover some Immunity. Antibiotics:
Speeds up healing of Colds, Pneumonia, Infection and Stomach Flu. Can cause Nausea if abused. Caffeine Pills:
Relieves Sleepiness. Can cause Shivers if abused. Antihistamines:
Relieves Congestion. Can cause Sleepiness if abused. Antipyretics:
Relieves a traditional Fever. Can cause Nausea if abused. Antiemetics:
Relieves Nausea. Cough Syrup:
Relieves a Sore Throat, may also make you Drunk if taken in large quantities. Flu Vaccine Vial:
A vial containing a Vaccine for the Flu Virus. Can be added to a syringe so that you can administer a Flu Shot. Each Vial can fill a Syringe 4 times. Taking a Flu Shot will cause the Severity of Flu to begin to decline and will provide you with a month of immunity to the Flu Virus. Common Infection Vaccine Vial:
A vial containing a Vaccine for the Infection. Can be added to a syringe so that you can administer a Common Infection Shot. Each Vial can fill a Syringe 4 times. Taking a Common Infection Shot will cause the Severity of a Common Infection to decline and will provide you with a month of immunity to the Common Infection. Rabies Vaccine:
A vial containing a Vaccine for the Rabies Virus. Can be added to a syringe so that you can administer a Rabies Shot. Each Vial Can fill a Syringe 4 times. Taking a Common Infection Shot will cure Rabies, provided you take it prior to the manifestation of symptoms, and will provide you with a month of immunity to the Rabies Virus.  
There are a few others I'd like such as Morphine and so on that would have a chance to cause addiction, but the ones I've added are more to expand on what is present, rather than add too much new.
 
Items:
Pill Dispenser:
A container with random pills inside. Water bottle with Dissolved Painkiller:
As the name suggests. The Player can dissolve up to 4 units of Painkillers into a Water Bottle, allowing for Painkiller use to be stretched out, if a bit weakened. Surgical Mask:
Surgical Masks (along with gasmasks) provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, as long as they are at least 50% clean with no damage. Hazmat Gear:
A full set of Hazmat Gear will provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, so long as they are undamaged. Syringe:
A medical syringe used for injecting yourself with a Vaccine. Maybe also for Addictive Drugs. Empty Vial:
Garbage item left over when adding a Vaccine to a Syringe. Can hold water.  
Traits:
Strong Immune System:
Chance of catching a disease is halved. Can go well with Iron Gut and Outdoorsman for a Robust Genetics build. Weak Immune System:
Replaces Prone To Illness. Chance of catching a disease is doubled, more likely for a wound to be infected and faster Zombification. Iron Gut:
Chance of catching Stomach Flu from food or water is halved. Weak Stomach:
Chance of catching Stomach Flu doubled. Outdoorsman:
Being wet does not weaken your Immune System. Immune to Hayfever. Allergy Prone:
Very prone to Hayfever. Hayfever gained this way bypasses Immune System Variable with there always being a 10% chance of contracting Hayfever when moving through thick Vegetation in off seasons and a 25% chance in Spring. Resilient:
Less likely for wounds to become infected and slows Zombification. Asthmatic:
40% increase in running endurance loss, 30% increase in swing endurance lost and a chance to loudly cough when Exerted. Hypochondriac:
May develop infection symptoms without being infected. Easily Amused:
Slower rate of boredom and unhappiness. Depression:
Becomes bored faster and gradually becomes sadder with time.  
The Immune System:
The Immune System, or simply just the Immunity variable, determines the chance of becoming ill.
At 0%, you are fully healthy and won't get sick.
But any activity while Sick, Dirty, Bloody, Wet, Sleepy, Exerted, Sad, Injured or Hungry will cause it to gradually rise. At 1%, you have a 1% chance of catching a disease and so on.
Sleeping will help you recover your Immunity most of the time, however putting yourself to sleep with Sleeping Pills or Alcohol will prevent this recovery. Being well fed will also help you recover.
This variable is invisible to the player, as it is to a real person.
 
Severity:
When catching a disease, it will gradually rise in severity, before reaching a peak and lowering again in severity until the disease is gone. During this time, all you can do is treat symptoms and rest until you are better. There are 4 levels of Severity, based on when the disease's variable is at 1%-25%, 26%-50%, 51%-75% and 76%-100%.
Certain diseases, when treated with certain medications and the disease's variable reaches 0% will then be cured.
 
Nutrients:
There are many nutrients which a player will gain with a balanced diet. Lacking certain nutrients in your diet for too long will result in a Nutritional Disease. Nutritional Diseases bypass the immune system.
Calories:
Calories are the main weight determining nutrient. This value must be balanced with hunger consistently, or else obesity or anorexia may sneak up on the player.
Maximum: 3700
Minimum: -2200 Carbohydrates:
Carbohydrates are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Carbohydrates, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Lipids:
Lipids, previously called fats, are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Lipids, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Proteins:
Proteins are a determining factor in the increase and decrease of the Player's strength stat. Without the necessary proteins, the player will not be able to level up their strength. If a player consumes more than 400 Protein units, they will increase their strength in the same way as in the same manner as B40/B41. If the player consumes more than 700 Protein units, they will gain a 1.5 multiplier for strength increase. If a player's protein units falls below -250, they will start to lose strength, and reaching the minimum Protein units of -500 will result in the loss of strength with a multiplier of 2.
Maximum: 1000
Minimum: -500 Salts:
Salts can alter the rate at which a player becomes thirsty. This value is ignored unless the player has consumed more than 400 or 700 Salts resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Sugars:
Sugars are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Sugars, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Vitamins:
Vitamins are essential for keeping your Immune System strong. So long as the player consumes more than 400 Vitamins, their Immunity will recover as per normal while resting or sleeping. If the Sugar unit falls below 0, their Immunity will no longer recover.
Maximum: 500
Minimum: -500  
Diseases:
Diseases are visible in the Health tab when you have a certain level of First-Aid, but otherwise you'll have to guess by symptoms and circumstances.
Flu:
Sometimes, Zombies, Pigs (when added) or Chickens (when added) will spawn as infected with the Flu Virus. Being within 5 tiles from an infected zombie, the infected Zombie's corpse, an infected Player, an infected Player's corpse, an infected Pig or Chicken and an infected Pig or Chicken's corpse will make you vulnerable to catching the flu. Pigs and Chickens will also be at risk of catching it.
Symptoms are Congestion, Fever, Pain and a Sore Throat.
After catching Flu, there is a cooldown time before you can catch it again of around a month.
Severity 1:
The Flu is Asymptomatic at this severity, increasing the likelihood that you will spread it to other players unwittingly.
Severity 2:
Level 2 symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms, risk of death without treatment.
  Cold:
A cold is an ambient bacterial infection that can be caught when being wet, hot, cold or tired. Similar to Flu but far less severe but also far quicker to show symptoms.
Symptoms are Congestion, Fever and a Sore Throat.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Congestion and Sore Throat, no Fever.
Severity 2:
Level 2 Congestion and Sore Throat, no Fever.
Severity 3:
Level 3 Congestion and Sore Throat, Level 1 Fever.
Severity 4:
Level 4 Congestion and Sore Throat, Level 2 Fever.
  Pneumonia:
An ambient infection of the lungs that can be caught while Hypothermic. Similar to a Cold but far more severe.
Symptoms are Fever, Sore Throat and Shivers.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Sore Throat and Shivers, no Fever.
Severity  2:
Level 2 Sore Throat, Shivers and Fever.
Severity 3:
Level 3 Sore Throat, Shivers and Fever.
Severity 4
Level 4 Sore Throat, Shivers and Fever. Risk of death without treatment.
  Hayfever:
Can be caught by moving through dense vegetation during Spring.
Symptoms are Congestion and a Sore Throat.
Can be treated directly with Antihistamines.
Severity 1:
Level 1 Congestion, no sore throat.
Severity 2:
Level 2 Congestion, no Sore Throat.
Severity 3:
Level 3 Congestion, Level 1 Sore Throat.
Severity 4:
Level 4 Congestion, Level 2 Sore Throat.
  Stomach Flu:
An infection of the stomach lining, can be caught by eating uncooked or rotten food as well as drinking tainted water.
Symptoms are Nausea, Fever and Shivers.
Can be treated directly with Antibiotics.
Severity 1:
Level 1 Nausea, no Fever or Shivers.
Severity 2:
Level 2 Nausea, no Fever or Shivers.
Severity 3:
Level 3 Nausea, Fever and Shivers.
Severity 4:
Level 4 Nausea, Fever and Shivers. Risk of Death if untreated.
  Bleach Poisoning:
Bleach poisoning is a fast onset and fatal illness caused by directly drinking Bleach. It is always Severity 4.
Symptoms are Sore Throat, Pain, Anxiety, Shivers and gradual loss of Health.
Severity 4:
Level 4 Symptoms. Death is certain.
  Food Poisoning:
Food Poisoning is similar to Botulism but is caught by eating Poison Berries, Poison Mushrooms or food poisoned with Bleach.
Symptoms are Nausea, Sore Throat, Pain, Shivers and gradual loss of Health.
Severity 1:
Level 1 Nausea and Sore Throat, no others.
Severity 2:
Level 2 Nausea and Sore Throat, Level 1 Pain and Shivers. No loss of Health.
Severity 3:
Level 3 Nausea and Sore Throat, Level 2 Pain and Shivers. No loss of Health.
Severity 4:
Level 4 Nausea, Sore Throat, Pain, Shivers and a gradual Loss of Health. Can be fatal even with treatment if health already low.
  Rabies:
Caught by being Bitten by an infected animal. It is always Fatal if not treated with a Rabies Vaccine prior to Severity 2.
Symptoms are Anger, Stress, Weakness, Sore Throat, Agoraphobia, Pain when Drinking or Eating and Gradual Loss of Health.
Severity 1:
No symptoms.
Severity 2:
Level 2 Symptoms, but no loss of Health.
Severity 3:
Level 3 Symptoms, but no loss of Health.
Severity 4:
Level 4 symptoms and gradual loss of Health. Death is certain.
  Infection:
Caught by not properly treating a wound or spending a lot of time around corpses while your immune system is compromised.
Symptoms are Nausea, Pain, Shivers and Fever. If playing as a Hypochondriac, the symptoms are identical to Zombification if contracted from a Zombie Scratch instead but not always fatal.
Can be directly treated with Antibiotics or applying a sterilizing agent to the infected wound.
Severity 1:
Level 1 Nausea, no other symptoms.
Severity 2:
Level 2 Symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms. Can be fatal if left untreated.
  Scurvy:
Scurvy is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Vitamin intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Scurvy. Taking in the proper amount of Vitamins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Shivers, Pain and gradual loss of Health.
Can be directly treated with food rich in Vitamins or Vitamins medication.
Severity 1:
Level 1 Shivers and Pain, no loss of Health.
Severity 2:
Level 2 Shivers and Pain, no loss of Health.
Severity 3:
Level 3 Shivers and Pain, no loss of Health.
Severity 4:
Level 4 Shivers and Pain and the gradual loss of Health. Can be fatal if left untreated.
  Anemia:
Anemia is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Protein intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Anemia. Taking in the proper amount of Proteins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sleepiness, Weakness, Decreased Spatial Awareness, lowered item transfer rate and the gradual loss of Health.
Can be directly treated with food rich in Proteins.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Thyroditis:
Thyroditis is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Salt intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Thyroditis. Taking in the proper amount of Saltss will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sore Throat, Shivers and the gradual loss of Health.
Can be directly treated with food rich in Salts.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Zombification:
Caught by being Bitten or Scratched by a Zombie. It bypasses Immune system, with Bites always resulting in being infected and a 25% chance of being infected by a Scratch.
Symptoms are Stress, Sadness, Nausea, Untreatable Fever and the eventual death and rising as a Zombie.
Severity 1:
Level 1 Stress, no other Symptoms.
Severity 2:
Level 2 Stress, Level 1 Sadness, no other Symptoms.
Severity 3:
Level 3 Stress, Nausea, Sadness and Fever.
Severity 4:
Level 4 Stress, Nausea, Sadness and Fever. Death is certain.  
Abilities:
Players with high First-Aid or medical related Occupations/Traits will be able to deduce illnesses and administer medication directly to another Player, so Doctors and Nurses will have even more use in Multiplayer.
 
And that's that! Did I miss anything? What did y'all think?

Needing forks, plates and other things to eat is just needless micro managing for a gameplay mechanic that wouldn't be in any way enjoyable to play as.

People eat the same foods on a daily basis all the time over the world. When you're dealing with surviving on a day to day basis, eating boiled/roasted potato every single day isn't as bad as you make it out to be when the alternative is starving. Boring food is also already in the game in regards to the (very underdeveloped) depression system.

Eating dirty plates won't make you sick in real life. All it takes is one rag to clean off a plate or a pan via scraping some gunk off. Again, it's micro for a mechanic that doesn't need it.

When selecting an item of clothing for Character Creation, all the clothing colours reset even if you had just manually set the colours.

This is really handy! Thanks @Okamikurainya

For the use of map additions and such, so you know where to place things.
Up to date with current version, you'll need to resave it as a .BMP to use it in WorldEd.

BASE PREVIEW:

 
BASE DOWNLOAD:
https://drive.google.com/file/d/1yNOj2HtOG1MNaBMENLXDru6ecacm8Qjv/view
 
VEGETATION PREVIEW:

 
VEGETATION DOWNLOAD:
https://drive.google.com/file/d/12gGjdu89LATwgqZELu4EFfh47XlxwWyz/view

Seasonal crops would indeed be nice, have certain crops only be able to grow in their assigned seasons while quickly withering in the off seasons.
Lowering seed gathering for "Seed-Bearing Crops" to just 2 and lowering the window to harvest them may help as well.

Another thing could be the addition of Berry Bushes. While you could still forage for berries, perhaps they will be less likely to be fresh as you're finding them on the ground, as opposed to a bush where they will remain fresh for a greater amount of time, having fruiting bushes occur at certain intervals in the appropriate seasons.

I always thought PZ would eventually reach the point where dealing with illness is a very real threat to long term survival. We all know that doctors are going to be in high demand once the apocalypse happens. This makes total sense. 

Right now, the way disease is handled contrasts starkly with the overall complexity of the game...

My suggestion is to remove the ambiguity and turn certain Moodles into Symptoms, rather than have them as the disease themselves.
 
Symptoms:
Congestion:
Congestion replaces the Cold Moodle, becoming a symptom. It functions near identically, giving the player a chance to sneeze loudly, attracting zombies. Can be aided with an equipped tissue and treated with Antihistamines.
"Runny Nose"
"The sniffles"
"Congested"
"Severe Congestion" Fever:
Fever replaces the current Sick Moodle, becoming a symptom. Each stage will increase your character's temperature by a certain amount and will cause damage on its' highest level while also lowering healing, strength and increasing the rate at which a player gets sleepy. Can be treated with Antipyretics unless it is a symptom of Zombification. Equipping a Cold Pack that has been cooled in a freezer or a bag of Frozen Peas can also help.
"Bit of a Temperature"
"Temperature"
"Severe Temperature"
"Terminal Fever" Nausea:
Nausea is the other half of the current Sick Moodle becoming a symptom in its' own right. It lowers healing, strength and speed. It can be treated with Antiemetics.
"Bit Sick"
"Sick"
"Really Sick"
"Severe Nausea" Sore Throat:
A Sore Throat is similar to Congestion, but may cause pain when eating with an increasing chance to loudly cough which may attract nearby zombies. Can be treated with Cough Syrup.
"Scratchy Throat"
"Painful Throat"
"Rough Cough"
"Severe Coughing" Shivers:
Shivering which will lower the accuracy of the player. Can be relieved with Painkillers.
"A bit Shaky"
"Shaky"
"Shivering"
"Severe Shivering"  
While those are direct symptoms, other Moodles such as Pain would also be symptoms, directly or indirectly.

Medications:
Painkillers:
Relieves Pain and Shivers. Can cause Nausea if abused. Beta Blockers:
Relieves Panic. Antidepressants:
Relieves Sadness. Can cause Anger if abused. Sleeping Tablets:
Helps you sleep. Can cause Nausea or loss of Health if abused or taken while Drunk. Vitamins:
These should boost healing and help you recover some Immunity. Antibiotics:
Speeds up healing of Colds, Pneumonia, Infection and Stomach Flu. Can cause Nausea if abused. Caffeine Pills:
Relieves Sleepiness. Can cause Shivers if abused. Antihistamines:
Relieves Congestion. Can cause Sleepiness if abused. Antipyretics:
Relieves a traditional Fever. Can cause Nausea if abused. Antiemetics:
Relieves Nausea. Cough Syrup:
Relieves a Sore Throat, may also make you Drunk if taken in large quantities. Flu Vaccine Vial:
A vial containing a Vaccine for the Flu Virus. Can be added to a syringe so that you can administer a Flu Shot. Each Vial can fill a Syringe 4 times. Taking a Flu Shot will cause the Severity of Flu to begin to decline and will provide you with a month of immunity to the Flu Virus. Common Infection Vaccine Vial:
A vial containing a Vaccine for the Infection. Can be added to a syringe so that you can administer a Common Infection Shot. Each Vial can fill a Syringe 4 times. Taking a Common Infection Shot will cause the Severity of a Common Infection to decline and will provide you with a month of immunity to the Common Infection. Rabies Vaccine:
A vial containing a Vaccine for the Rabies Virus. Can be added to a syringe so that you can administer a Rabies Shot. Each Vial Can fill a Syringe 4 times. Taking a Common Infection Shot will cure Rabies, provided you take it prior to the manifestation of symptoms, and will provide you with a month of immunity to the Rabies Virus.  
There are a few others I'd like such as Morphine and so on that would have a chance to cause addiction, but the ones I've added are more to expand on what is present, rather than add too much new.
 
Items:
Pill Dispenser:
A container with random pills inside. Water bottle with Dissolved Painkiller:
As the name suggests. The Player can dissolve up to 4 units of Painkillers into a Water Bottle, allowing for Painkiller use to be stretched out, if a bit weakened. Surgical Mask:
Surgical Masks (along with gasmasks) provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, as long as they are at least 50% clean with no damage. Hazmat Gear:
A full set of Hazmat Gear will provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, so long as they are undamaged. Syringe:
A medical syringe used for injecting yourself with a Vaccine. Maybe also for Addictive Drugs. Empty Vial:
Garbage item left over when adding a Vaccine to a Syringe. Can hold water.  
Traits:
Strong Immune System:
Chance of catching a disease is halved. Can go well with Iron Gut and Outdoorsman for a Robust Genetics build. Weak Immune System:
Replaces Prone To Illness. Chance of catching a disease is doubled, more likely for a wound to be infected and faster Zombification. Iron Gut:
Chance of catching Stomach Flu from food or water is halved. Weak Stomach:
Chance of catching Stomach Flu doubled. Outdoorsman:
Being wet does not weaken your Immune System. Immune to Hayfever. Allergy Prone:
Very prone to Hayfever. Hayfever gained this way bypasses Immune System Variable with there always being a 10% chance of contracting Hayfever when moving through thick Vegetation in off seasons and a 25% chance in Spring. Resilient:
Less likely for wounds to become infected and slows Zombification. Asthmatic:
40% increase in running endurance loss, 30% increase in swing endurance lost and a chance to loudly cough when Exerted. Hypochondriac:
May develop infection symptoms without being infected. Easily Amused:
Slower rate of boredom and unhappiness. Depression:
Becomes bored faster and gradually becomes sadder with time.  
The Immune System:
The Immune System, or simply just the Immunity variable, determines the chance of becoming ill.
At 0%, you are fully healthy and won't get sick.
But any activity while Sick, Dirty, Bloody, Wet, Sleepy, Exerted, Sad, Injured or Hungry will cause it to gradually rise. At 1%, you have a 1% chance of catching a disease and so on.
Sleeping will help you recover your Immunity most of the time, however putting yourself to sleep with Sleeping Pills or Alcohol will prevent this recovery. Being well fed will also help you recover.
This variable is invisible to the player, as it is to a real person.
 
Severity:
When catching a disease, it will gradually rise in severity, before reaching a peak and lowering again in severity until the disease is gone. During this time, all you can do is treat symptoms and rest until you are better. There are 4 levels of Severity, based on when the disease's variable is at 1%-25%, 26%-50%, 51%-75% and 76%-100%.
Certain diseases, when treated with certain medications and the disease's variable reaches 0% will then be cured.
 
Nutrients:
There are many nutrients which a player will gain with a balanced diet. Lacking certain nutrients in your diet for too long will result in a Nutritional Disease. Nutritional Diseases bypass the immune system.
Calories:
Calories are the main weight determining nutrient. This value must be balanced with hunger consistently, or else obesity or anorexia may sneak up on the player.
Maximum: 3700
Minimum: -2200 Carbohydrates:
Carbohydrates are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Carbohydrates, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Lipids:
Lipids, previously called fats, are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Lipids, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Proteins:
Proteins are a determining factor in the increase and decrease of the Player's strength stat. Without the necessary proteins, the player will not be able to level up their strength. If a player consumes more than 400 Protein units, they will increase their strength in the same way as in the same manner as B40/B41. If the player consumes more than 700 Protein units, they will gain a 1.5 multiplier for strength increase. If a player's protein units falls below -250, they will start to lose strength, and reaching the minimum Protein units of -500 will result in the loss of strength with a multiplier of 2.
Maximum: 1000
Minimum: -500 Salts:
Salts can alter the rate at which a player becomes thirsty. This value is ignored unless the player has consumed more than 400 or 700 Salts resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Sugars:
Sugars are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Sugars, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Vitamins:
Vitamins are essential for keeping your Immune System strong. So long as the player consumes more than 400 Vitamins, their Immunity will recover as per normal while resting or sleeping. If the Sugar unit falls below 0, their Immunity will no longer recover.
Maximum: 500
Minimum: -500  
Diseases:
Diseases are visible in the Health tab when you have a certain level of First-Aid, but otherwise you'll have to guess by symptoms and circumstances.
Flu:
Sometimes, Zombies, Pigs (when added) or Chickens (when added) will spawn as infected with the Flu Virus. Being within 5 tiles from an infected zombie, the infected Zombie's corpse, an infected Player, an infected Player's corpse, an infected Pig or Chicken and an infected Pig or Chicken's corpse will make you vulnerable to catching the flu. Pigs and Chickens will also be at risk of catching it.
Symptoms are Congestion, Fever, Pain and a Sore Throat.
After catching Flu, there is a cooldown time before you can catch it again of around a month.
Severity 1:
The Flu is Asymptomatic at this severity, increasing the likelihood that you will spread it to other players unwittingly.
Severity 2:
Level 2 symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms, risk of death without treatment.
  Cold:
A cold is an ambient bacterial infection that can be caught when being wet, hot, cold or tired. Similar to Flu but far less severe but also far quicker to show symptoms.
Symptoms are Congestion, Fever and a Sore Throat.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Congestion and Sore Throat, no Fever.
Severity 2:
Level 2 Congestion and Sore Throat, no Fever.
Severity 3:
Level 3 Congestion and Sore Throat, Level 1 Fever.
Severity 4:
Level 4 Congestion and Sore Throat, Level 2 Fever.
  Pneumonia:
An ambient infection of the lungs that can be caught while Hypothermic. Similar to a Cold but far more severe.
Symptoms are Fever, Sore Throat and Shivers.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Sore Throat and Shivers, no Fever.
Severity  2:
Level 2 Sore Throat, Shivers and Fever.
Severity 3:
Level 3 Sore Throat, Shivers and Fever.
Severity 4
Level 4 Sore Throat, Shivers and Fever. Risk of death without treatment.
  Hayfever:
Can be caught by moving through dense vegetation during Spring.
Symptoms are Congestion and a Sore Throat.
Can be treated directly with Antihistamines.
Severity 1:
Level 1 Congestion, no sore throat.
Severity 2:
Level 2 Congestion, no Sore Throat.
Severity 3:
Level 3 Congestion, Level 1 Sore Throat.
Severity 4:
Level 4 Congestion, Level 2 Sore Throat.
  Stomach Flu:
An infection of the stomach lining, can be caught by eating uncooked or rotten food as well as drinking tainted water.
Symptoms are Nausea, Fever and Shivers.
Can be treated directly with Antibiotics.
Severity 1:
Level 1 Nausea, no Fever or Shivers.
Severity 2:
Level 2 Nausea, no Fever or Shivers.
Severity 3:
Level 3 Nausea, Fever and Shivers.
Severity 4:
Level 4 Nausea, Fever and Shivers. Risk of Death if untreated.
  Bleach Poisoning:
Bleach poisoning is a fast onset and fatal illness caused by directly drinking Bleach. It is always Severity 4.
Symptoms are Sore Throat, Pain, Anxiety, Shivers and gradual loss of Health.
Severity 4:
Level 4 Symptoms. Death is certain.
  Food Poisoning:
Food Poisoning is similar to Botulism but is caught by eating Poison Berries, Poison Mushrooms or food poisoned with Bleach.
Symptoms are Nausea, Sore Throat, Pain, Shivers and gradual loss of Health.
Severity 1:
Level 1 Nausea and Sore Throat, no others.
Severity 2:
Level 2 Nausea and Sore Throat, Level 1 Pain and Shivers. No loss of Health.
Severity 3:
Level 3 Nausea and Sore Throat, Level 2 Pain and Shivers. No loss of Health.
Severity 4:
Level 4 Nausea, Sore Throat, Pain, Shivers and a gradual Loss of Health. Can be fatal even with treatment if health already low.
  Rabies:
Caught by being Bitten by an infected animal. It is always Fatal if not treated with a Rabies Vaccine prior to Severity 2.
Symptoms are Anger, Stress, Weakness, Sore Throat, Agoraphobia, Pain when Drinking or Eating and Gradual Loss of Health.
Severity 1:
No symptoms.
Severity 2:
Level 2 Symptoms, but no loss of Health.
Severity 3:
Level 3 Symptoms, but no loss of Health.
Severity 4:
Level 4 symptoms and gradual loss of Health. Death is certain.
  Infection:
Caught by not properly treating a wound or spending a lot of time around corpses while your immune system is compromised.
Symptoms are Nausea, Pain, Shivers and Fever. If playing as a Hypochondriac, the symptoms are identical to Zombification if contracted from a Zombie Scratch instead but not always fatal.
Can be directly treated with Antibiotics or applying a sterilizing agent to the infected wound.
Severity 1:
Level 1 Nausea, no other symptoms.
Severity 2:
Level 2 Symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms. Can be fatal if left untreated.
  Scurvy:
Scurvy is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Vitamin intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Scurvy. Taking in the proper amount of Vitamins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Shivers, Pain and gradual loss of Health.
Can be directly treated with food rich in Vitamins or Vitamins medication.
Severity 1:
Level 1 Shivers and Pain, no loss of Health.
Severity 2:
Level 2 Shivers and Pain, no loss of Health.
Severity 3:
Level 3 Shivers and Pain, no loss of Health.
Severity 4:
Level 4 Shivers and Pain and the gradual loss of Health. Can be fatal if left untreated.
  Anemia:
Anemia is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Protein intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Anemia. Taking in the proper amount of Proteins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sleepiness, Weakness, Decreased Spatial Awareness, lowered item transfer rate and the gradual loss of Health.
Can be directly treated with food rich in Proteins.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Thyroditis:
Thyroditis is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Salt intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Thyroditis. Taking in the proper amount of Saltss will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sore Throat, Shivers and the gradual loss of Health.
Can be directly treated with food rich in Salts.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Zombification:
Caught by being Bitten or Scratched by a Zombie. It bypasses Immune system, with Bites always resulting in being infected and a 25% chance of being infected by a Scratch.
Symptoms are Stress, Sadness, Nausea, Untreatable Fever and the eventual death and rising as a Zombie.
Severity 1:
Level 1 Stress, no other Symptoms.
Severity 2:
Level 2 Stress, Level 1 Sadness, no other Symptoms.
Severity 3:
Level 3 Stress, Nausea, Sadness and Fever.
Severity 4:
Level 4 Stress, Nausea, Sadness and Fever. Death is certain.  
Abilities:
Players with high First-Aid or medical related Occupations/Traits will be able to deduce illnesses and administer medication directly to another Player, so Doctors and Nurses will have even more use in Multiplayer.
 
And that's that! Did I miss anything? What did y'all think?

NEW
All characters now start with a belt - giving them a "Back" slot & two belt (left/right) belt slots.
You can either right click a slot, or drag & drop a weapon to it.  Or, alternatively, click a weapon in your inventory to attach it to the hotbar.
Weapons will be shown on the player. Pressing a hotkey (from 1 to 5) will auto equip the weapon assigned to each slot.
This is a work in progress system that we'd love feedback on!
Added holsters
Holsters have a chance to spawn on police/policestate zombies (automatic get one if he had a gun)
- Rebuilt ProjectZomboid.exe as a gui application, no more console window. Should work with Steam remote play together now.
- Added player Bob_VaultOverToFall animation when climbing over fences.
- Added zombie Zombie_WalkTrees animation for walktoward and pathfind states.
- Zombie lunge animations played at 50% speed in trees.

BALANCE

- Boosted wood axe damage, speed, amount of time you can move during strafe, to make it a viable (but still quite slow) heavy damage weapon
- Force standing when drinking/filling items from sink.
- Reduced handgun model size (+ muzzle redone)
- Added Chipped stone to craft lance recipe.
- Made tall fences transparent when the player is behind them
- Disabled Hypochondriac trait until it can be fully reworked
- Reload XP now given when inserting bullets in clip (small chance) and when reloading (bigger chance).
- Added spear fishing.
- Now equip in 2 hands shovel when taking dirt/sands..
- Added Griddle pan for stir-fry.

FIXES

- Fixed zombies spawning in buildings long after a player has entered the building. 
- Fixed Double-barrel shotgun issues.
  1) Missing inventory icon.
  2) Removed chamber, which allowed 3 shells to be loaded.
  3) Racking not required.
- Fixed blob/suitcase Zeds on spawn
- Fixed FMOD crash on 64-bit.
 Java_fmod_javafmodJNI_FMOD_1System_1CreateChannelGroup() was casting a pointer to 'long' when it needed to be a 64-bit 'long long'.
 SoundManager was calling FMOD_Channel_SetPaused() instead of FMOD_ChannelGroup_SetPaused().
- Fixed zombies getting stuck in the air after climbing through a window.
- Fixed exception after renaming food to have a dollar-sign character in it.
- Fixed lua error when taking compost from a composter.
- Fixed zombified players interacting with doors/windows/etc by left-clicking.
- Fixed new shovels not being useable for taking dirt/gravel/sand.
- Fixed hammering animation when pouring dirt/gravel/sand from a bag.
- Fixed Logs.zip console.txts are limited to all of 2 lines during most crashes
- Fixed issues pressing Escape while entering or exiting a vehicle, or switching seats.
- Fixed players going through a wall when run-vaulting over a fence adjacent to the wall.
- Fixed issue: Unhandled Thread exception by the SQLDB in a non UTF8 environ.
- Fixed Protection screen not working with a controller.
- Fixed Info hair/beard buttons not working with a controller.
- Fixed clothing dryer and washer continuing to play sound after the power goes out.
- Fixed weather mask not updating when the zoom level changes.
- Fixed weather mask not rendering for splitscreen players.
- Fixed zombies get stuck after climbing over a fence with no floor on the other side.
- Fixed some files being closed via garbage collection.
- Crouch key only affects player 0 which fixes split-screen shared crouch
- Fixed "Sit On Ground" context-menu option is available when already sitting.
- Fixed "Sit On Ground" context-menu option is not available when using a controller.
- Fixed adding frozen food into recipes.
- Fixed old Socks still existing.

1061: Small chance to yell out in fear when suddenly stumbling upon a zombie and getting the Panic Moodle, with a larger chance for it to happen with Cowardly Characters. This may attract more Zombies.

Normal Viral diseases ( cold )  you don't give Anti Virals ( unless they are suffering from an immunicompromised state  )
You generally only give it in cases like Herpes \ Encephalitis \ etc.
 
Rabies requires hospitalization it isn't something you treat walking around. It is an unnecessary mechanic that has no game play value unless it was a management style game.
 
General treatment for standard viral diseases is just supportive therapy. 
 

Compared to the complexity of other systems, upcoming and implemented, I've felt the current medical system is not as indepth as it could be. This proposed system I feel, even if half implemented, would improve it.
 
If only because it'd make Medical professions and/or medical traits a stronger pick if it came with the ability to diagnose illnesses. 

Hope that this will see the day of integration! The current system really is (compared to the others) kinda bland.
 
In the new Thursdoid the showed the insulation system and this again shows the lack of depth to the diseases.

Would be also good to have some antivirals to help treat viral diseases like flu and Anti-rabid vaccines.
 
Other than that, all of this is pretty freakin' great.

Wow! This is definetly well thought out and phrased suggestion. Having variety and more complexity on the disease system would be very welcome.

Right now, the way disease is handled contrasts starkly with the overall complexity of the game...

My suggestion is to remove the ambiguity and turn certain Moodles into Symptoms, rather than have them as the disease themselves.
 
Symptoms:
Congestion:
Congestion replaces the Cold Moodle, becoming a symptom. It functions near identically, giving the player a chance to sneeze loudly, attracting zombies. Can be aided with an equipped tissue and treated with Antihistamines.
"Runny Nose"
"The sniffles"
"Congested"
"Severe Congestion" Fever:
Fever replaces the current Sick Moodle, becoming a symptom. Each stage will increase your character's temperature by a certain amount and will cause damage on its' highest level while also lowering healing, strength and increasing the rate at which a player gets sleepy. Can be treated with Antipyretics unless it is a symptom of Zombification. Equipping a Cold Pack that has been cooled in a freezer or a bag of Frozen Peas can also help.
"Bit of a Temperature"
"Temperature"
"Severe Temperature"
"Terminal Fever" Nausea:
Nausea is the other half of the current Sick Moodle becoming a symptom in its' own right. It lowers healing, strength and speed. It can be treated with Antiemetics.
"Bit Sick"
"Sick"
"Really Sick"
"Severe Nausea" Sore Throat:
A Sore Throat is similar to Congestion, but may cause pain when eating with an increasing chance to loudly cough which may attract nearby zombies. Can be treated with Cough Syrup.
"Scratchy Throat"
"Painful Throat"
"Rough Cough"
"Severe Coughing" Shivers:
Shivering which will lower the accuracy of the player. Can be relieved with Painkillers.
"A bit Shaky"
"Shaky"
"Shivering"
"Severe Shivering"  
While those are direct symptoms, other Moodles such as Pain would also be symptoms, directly or indirectly.

Medications:
Painkillers:
Relieves Pain and Shivers. Can cause Nausea if abused. Beta Blockers:
Relieves Panic. Antidepressants:
Relieves Sadness. Can cause Anger if abused. Sleeping Tablets:
Helps you sleep. Can cause Nausea or loss of Health if abused or taken while Drunk. Vitamins:
These should boost healing and help you recover some Immunity. Antibiotics:
Speeds up healing of Colds, Pneumonia, Infection and Stomach Flu. Can cause Nausea if abused. Caffeine Pills:
Relieves Sleepiness. Can cause Shivers if abused. Antihistamines:
Relieves Congestion. Can cause Sleepiness if abused. Antipyretics:
Relieves a traditional Fever. Can cause Nausea if abused. Antiemetics:
Relieves Nausea. Cough Syrup:
Relieves a Sore Throat, may also make you Drunk if taken in large quantities. Flu Vaccine Vial:
A vial containing a Vaccine for the Flu Virus. Can be added to a syringe so that you can administer a Flu Shot. Each Vial can fill a Syringe 4 times. Taking a Flu Shot will cause the Severity of Flu to begin to decline and will provide you with a month of immunity to the Flu Virus. Common Infection Vaccine Vial:
A vial containing a Vaccine for the Infection. Can be added to a syringe so that you can administer a Common Infection Shot. Each Vial can fill a Syringe 4 times. Taking a Common Infection Shot will cause the Severity of a Common Infection to decline and will provide you with a month of immunity to the Common Infection. Rabies Vaccine:
A vial containing a Vaccine for the Rabies Virus. Can be added to a syringe so that you can administer a Rabies Shot. Each Vial Can fill a Syringe 4 times. Taking a Common Infection Shot will cure Rabies, provided you take it prior to the manifestation of symptoms, and will provide you with a month of immunity to the Rabies Virus.  
There are a few others I'd like such as Morphine and so on that would have a chance to cause addiction, but the ones I've added are more to expand on what is present, rather than add too much new.
 
Items:
Pill Dispenser:
A container with random pills inside. Water bottle with Dissolved Painkiller:
As the name suggests. The Player can dissolve up to 4 units of Painkillers into a Water Bottle, allowing for Painkiller use to be stretched out, if a bit weakened. Surgical Mask:
Surgical Masks (along with gasmasks) provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, as long as they are at least 50% clean with no damage. Hazmat Gear:
A full set of Hazmat Gear will provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, so long as they are undamaged. Syringe:
A medical syringe used for injecting yourself with a Vaccine. Maybe also for Addictive Drugs. Empty Vial:
Garbage item left over when adding a Vaccine to a Syringe. Can hold water.  
Traits:
Strong Immune System:
Chance of catching a disease is halved. Can go well with Iron Gut and Outdoorsman for a Robust Genetics build. Weak Immune System:
Replaces Prone To Illness. Chance of catching a disease is doubled, more likely for a wound to be infected and faster Zombification. Iron Gut:
Chance of catching Stomach Flu from food or water is halved. Weak Stomach:
Chance of catching Stomach Flu doubled. Outdoorsman:
Being wet does not weaken your Immune System. Immune to Hayfever. Allergy Prone:
Very prone to Hayfever. Hayfever gained this way bypasses Immune System Variable with there always being a 10% chance of contracting Hayfever when moving through thick Vegetation in off seasons and a 25% chance in Spring. Resilient:
Less likely for wounds to become infected and slows Zombification. Asthmatic:
40% increase in running endurance loss, 30% increase in swing endurance lost and a chance to loudly cough when Exerted. Hypochondriac:
May develop infection symptoms without being infected. Easily Amused:
Slower rate of boredom and unhappiness. Depression:
Becomes bored faster and gradually becomes sadder with time.  
The Immune System:
The Immune System, or simply just the Immunity variable, determines the chance of becoming ill.
At 0%, you are fully healthy and won't get sick.
But any activity while Sick, Dirty, Bloody, Wet, Sleepy, Exerted, Sad, Injured or Hungry will cause it to gradually rise. At 1%, you have a 1% chance of catching a disease and so on.
Sleeping will help you recover your Immunity most of the time, however putting yourself to sleep with Sleeping Pills or Alcohol will prevent this recovery. Being well fed will also help you recover.
This variable is invisible to the player, as it is to a real person.
 
Severity:
When catching a disease, it will gradually rise in severity, before reaching a peak and lowering again in severity until the disease is gone. During this time, all you can do is treat symptoms and rest until you are better. There are 4 levels of Severity, based on when the disease's variable is at 1%-25%, 26%-50%, 51%-75% and 76%-100%.
Certain diseases, when treated with certain medications and the disease's variable reaches 0% will then be cured.
 
Nutrients:
There are many nutrients which a player will gain with a balanced diet. Lacking certain nutrients in your diet for too long will result in a Nutritional Disease. Nutritional Diseases bypass the immune system.
Calories:
Calories are the main weight determining nutrient. This value must be balanced with hunger consistently, or else obesity or anorexia may sneak up on the player.
Maximum: 3700
Minimum: -2200 Carbohydrates:
Carbohydrates are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Carbohydrates, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Lipids:
Lipids, previously called fats, are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Lipids, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Proteins:
Proteins are a determining factor in the increase and decrease of the Player's strength stat. Without the necessary proteins, the player will not be able to level up their strength. If a player consumes more than 400 Protein units, they will increase their strength in the same way as in the same manner as B40/B41. If the player consumes more than 700 Protein units, they will gain a 1.5 multiplier for strength increase. If a player's protein units falls below -250, they will start to lose strength, and reaching the minimum Protein units of -500 will result in the loss of strength with a multiplier of 2.
Maximum: 1000
Minimum: -500 Salts:
Salts can alter the rate at which a player becomes thirsty. This value is ignored unless the player has consumed more than 400 or 700 Salts resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Sugars:
Sugars are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Sugars, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Vitamins:
Vitamins are essential for keeping your Immune System strong. So long as the player consumes more than 400 Vitamins, their Immunity will recover as per normal while resting or sleeping. If the Sugar unit falls below 0, their Immunity will no longer recover.
Maximum: 500
Minimum: -500  
Diseases:
Diseases are visible in the Health tab when you have a certain level of First-Aid, but otherwise you'll have to guess by symptoms and circumstances.
Flu:
Sometimes, Zombies, Pigs (when added) or Chickens (when added) will spawn as infected with the Flu Virus. Being within 5 tiles from an infected zombie, the infected Zombie's corpse, an infected Player, an infected Player's corpse, an infected Pig or Chicken and an infected Pig or Chicken's corpse will make you vulnerable to catching the flu. Pigs and Chickens will also be at risk of catching it.
Symptoms are Congestion, Fever, Pain and a Sore Throat.
After catching Flu, there is a cooldown time before you can catch it again of around a month.
Severity 1:
The Flu is Asymptomatic at this severity, increasing the likelihood that you will spread it to other players unwittingly.
Severity 2:
Level 2 symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms, risk of death without treatment.
  Cold:
A cold is an ambient bacterial infection that can be caught when being wet, hot, cold or tired. Similar to Flu but far less severe but also far quicker to show symptoms.
Symptoms are Congestion, Fever and a Sore Throat.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Congestion and Sore Throat, no Fever.
Severity 2:
Level 2 Congestion and Sore Throat, no Fever.
Severity 3:
Level 3 Congestion and Sore Throat, Level 1 Fever.
Severity 4:
Level 4 Congestion and Sore Throat, Level 2 Fever.
  Pneumonia:
An ambient infection of the lungs that can be caught while Hypothermic. Similar to a Cold but far more severe.
Symptoms are Fever, Sore Throat and Shivers.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Sore Throat and Shivers, no Fever.
Severity  2:
Level 2 Sore Throat, Shivers and Fever.
Severity 3:
Level 3 Sore Throat, Shivers and Fever.
Severity 4
Level 4 Sore Throat, Shivers and Fever. Risk of death without treatment.
  Hayfever:
Can be caught by moving through dense vegetation during Spring.
Symptoms are Congestion and a Sore Throat.
Can be treated directly with Antihistamines.
Severity 1:
Level 1 Congestion, no sore throat.
Severity 2:
Level 2 Congestion, no Sore Throat.
Severity 3:
Level 3 Congestion, Level 1 Sore Throat.
Severity 4:
Level 4 Congestion, Level 2 Sore Throat.
  Stomach Flu:
An infection of the stomach lining, can be caught by eating uncooked or rotten food as well as drinking tainted water.
Symptoms are Nausea, Fever and Shivers.
Can be treated directly with Antibiotics.
Severity 1:
Level 1 Nausea, no Fever or Shivers.
Severity 2:
Level 2 Nausea, no Fever or Shivers.
Severity 3:
Level 3 Nausea, Fever and Shivers.
Severity 4:
Level 4 Nausea, Fever and Shivers. Risk of Death if untreated.
  Bleach Poisoning:
Bleach poisoning is a fast onset and fatal illness caused by directly drinking Bleach. It is always Severity 4.
Symptoms are Sore Throat, Pain, Anxiety, Shivers and gradual loss of Health.
Severity 4:
Level 4 Symptoms. Death is certain.
  Food Poisoning:
Food Poisoning is similar to Botulism but is caught by eating Poison Berries, Poison Mushrooms or food poisoned with Bleach.
Symptoms are Nausea, Sore Throat, Pain, Shivers and gradual loss of Health.
Severity 1:
Level 1 Nausea and Sore Throat, no others.
Severity 2:
Level 2 Nausea and Sore Throat, Level 1 Pain and Shivers. No loss of Health.
Severity 3:
Level 3 Nausea and Sore Throat, Level 2 Pain and Shivers. No loss of Health.
Severity 4:
Level 4 Nausea, Sore Throat, Pain, Shivers and a gradual Loss of Health. Can be fatal even with treatment if health already low.
  Rabies:
Caught by being Bitten by an infected animal. It is always Fatal if not treated with a Rabies Vaccine prior to Severity 2.
Symptoms are Anger, Stress, Weakness, Sore Throat, Agoraphobia, Pain when Drinking or Eating and Gradual Loss of Health.
Severity 1:
No symptoms.
Severity 2:
Level 2 Symptoms, but no loss of Health.
Severity 3:
Level 3 Symptoms, but no loss of Health.
Severity 4:
Level 4 symptoms and gradual loss of Health. Death is certain.
  Infection:
Caught by not properly treating a wound or spending a lot of time around corpses while your immune system is compromised.
Symptoms are Nausea, Pain, Shivers and Fever. If playing as a Hypochondriac, the symptoms are identical to Zombification if contracted from a Zombie Scratch instead but not always fatal.
Can be directly treated with Antibiotics or applying a sterilizing agent to the infected wound.
Severity 1:
Level 1 Nausea, no other symptoms.
Severity 2:
Level 2 Symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms. Can be fatal if left untreated.
  Scurvy:
Scurvy is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Vitamin intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Scurvy. Taking in the proper amount of Vitamins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Shivers, Pain and gradual loss of Health.
Can be directly treated with food rich in Vitamins or Vitamins medication.
Severity 1:
Level 1 Shivers and Pain, no loss of Health.
Severity 2:
Level 2 Shivers and Pain, no loss of Health.
Severity 3:
Level 3 Shivers and Pain, no loss of Health.
Severity 4:
Level 4 Shivers and Pain and the gradual loss of Health. Can be fatal if left untreated.
  Anemia:
Anemia is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Protein intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Anemia. Taking in the proper amount of Proteins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sleepiness, Weakness, Decreased Spatial Awareness, lowered item transfer rate and the gradual loss of Health.
Can be directly treated with food rich in Proteins.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Thyroditis:
Thyroditis is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Salt intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Thyroditis. Taking in the proper amount of Saltss will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sore Throat, Shivers and the gradual loss of Health.
Can be directly treated with food rich in Salts.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Zombification:
Caught by being Bitten or Scratched by a Zombie. It bypasses Immune system, with Bites always resulting in being infected and a 25% chance of being infected by a Scratch.
Symptoms are Stress, Sadness, Nausea, Untreatable Fever and the eventual death and rising as a Zombie.
Severity 1:
Level 1 Stress, no other Symptoms.
Severity 2:
Level 2 Stress, Level 1 Sadness, no other Symptoms.
Severity 3:
Level 3 Stress, Nausea, Sadness and Fever.
Severity 4:
Level 4 Stress, Nausea, Sadness and Fever. Death is certain.  
Abilities:
Players with high First-Aid or medical related Occupations/Traits will be able to deduce illnesses and administer medication directly to another Player, so Doctors and Nurses will have even more use in Multiplayer.
 
And that's that! Did I miss anything? What did y'all think?

Right now, the way disease is handled contrasts starkly with the overall complexity of the game...

My suggestion is to remove the ambiguity and turn certain Moodles into Symptoms, rather than have them as the disease themselves.
 
Symptoms:
Congestion:
Congestion replaces the Cold Moodle, becoming a symptom. It functions near identically, giving the player a chance to sneeze loudly, attracting zombies. Can be aided with an equipped tissue and treated with Antihistamines.
"Runny Nose"
"The sniffles"
"Congested"
"Severe Congestion" Fever:
Fever replaces the current Sick Moodle, becoming a symptom. Each stage will increase your character's temperature by a certain amount and will cause damage on its' highest level while also lowering healing, strength and increasing the rate at which a player gets sleepy. Can be treated with Antipyretics unless it is a symptom of Zombification. Equipping a Cold Pack that has been cooled in a freezer or a bag of Frozen Peas can also help.
"Bit of a Temperature"
"Temperature"
"Severe Temperature"
"Terminal Fever" Nausea:
Nausea is the other half of the current Sick Moodle becoming a symptom in its' own right. It lowers healing, strength and speed. It can be treated with Antiemetics.
"Bit Sick"
"Sick"
"Really Sick"
"Severe Nausea" Sore Throat:
A Sore Throat is similar to Congestion, but may cause pain when eating with an increasing chance to loudly cough which may attract nearby zombies. Can be treated with Cough Syrup.
"Scratchy Throat"
"Painful Throat"
"Rough Cough"
"Severe Coughing" Shivers:
Shivering which will lower the accuracy of the player. Can be relieved with Painkillers.
"A bit Shaky"
"Shaky"
"Shivering"
"Severe Shivering"  
While those are direct symptoms, other Moodles such as Pain would also be symptoms, directly or indirectly.

Medications:
Painkillers:
Relieves Pain and Shivers. Can cause Nausea if abused. Beta Blockers:
Relieves Panic. Antidepressants:
Relieves Sadness. Can cause Anger if abused. Sleeping Tablets:
Helps you sleep. Can cause Nausea or loss of Health if abused or taken while Drunk. Vitamins:
These should boost healing and help you recover some Immunity. Antibiotics:
Speeds up healing of Colds, Pneumonia, Infection and Stomach Flu. Can cause Nausea if abused. Caffeine Pills:
Relieves Sleepiness. Can cause Shivers if abused. Antihistamines:
Relieves Congestion. Can cause Sleepiness if abused. Antipyretics:
Relieves a traditional Fever. Can cause Nausea if abused. Antiemetics:
Relieves Nausea. Cough Syrup:
Relieves a Sore Throat, may also make you Drunk if taken in large quantities. Flu Vaccine Vial:
A vial containing a Vaccine for the Flu Virus. Can be added to a syringe so that you can administer a Flu Shot. Each Vial can fill a Syringe 4 times. Taking a Flu Shot will cause the Severity of Flu to begin to decline and will provide you with a month of immunity to the Flu Virus. Common Infection Vaccine Vial:
A vial containing a Vaccine for the Infection. Can be added to a syringe so that you can administer a Common Infection Shot. Each Vial can fill a Syringe 4 times. Taking a Common Infection Shot will cause the Severity of a Common Infection to decline and will provide you with a month of immunity to the Common Infection. Rabies Vaccine:
A vial containing a Vaccine for the Rabies Virus. Can be added to a syringe so that you can administer a Rabies Shot. Each Vial Can fill a Syringe 4 times. Taking a Common Infection Shot will cure Rabies, provided you take it prior to the manifestation of symptoms, and will provide you with a month of immunity to the Rabies Virus.  
There are a few others I'd like such as Morphine and so on that would have a chance to cause addiction, but the ones I've added are more to expand on what is present, rather than add too much new.
 
Items:
Pill Dispenser:
A container with random pills inside. Water bottle with Dissolved Painkiller:
As the name suggests. The Player can dissolve up to 4 units of Painkillers into a Water Bottle, allowing for Painkiller use to be stretched out, if a bit weakened. Surgical Mask:
Surgical Masks (along with gasmasks) provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, as long as they are at least 50% clean with no damage. Hazmat Gear:
A full set of Hazmat Gear will provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, so long as they are undamaged. Syringe:
A medical syringe used for injecting yourself with a Vaccine. Maybe also for Addictive Drugs. Empty Vial:
Garbage item left over when adding a Vaccine to a Syringe. Can hold water.  
Traits:
Strong Immune System:
Chance of catching a disease is halved. Can go well with Iron Gut and Outdoorsman for a Robust Genetics build. Weak Immune System:
Replaces Prone To Illness. Chance of catching a disease is doubled, more likely for a wound to be infected and faster Zombification. Iron Gut:
Chance of catching Stomach Flu from food or water is halved. Weak Stomach:
Chance of catching Stomach Flu doubled. Outdoorsman:
Being wet does not weaken your Immune System. Immune to Hayfever. Allergy Prone:
Very prone to Hayfever. Hayfever gained this way bypasses Immune System Variable with there always being a 10% chance of contracting Hayfever when moving through thick Vegetation in off seasons and a 25% chance in Spring. Resilient:
Less likely for wounds to become infected and slows Zombification. Asthmatic:
40% increase in running endurance loss, 30% increase in swing endurance lost and a chance to loudly cough when Exerted. Hypochondriac:
May develop infection symptoms without being infected. Easily Amused:
Slower rate of boredom and unhappiness. Depression:
Becomes bored faster and gradually becomes sadder with time.  
The Immune System:
The Immune System, or simply just the Immunity variable, determines the chance of becoming ill.
At 0%, you are fully healthy and won't get sick.
But any activity while Sick, Dirty, Bloody, Wet, Sleepy, Exerted, Sad, Injured or Hungry will cause it to gradually rise. At 1%, you have a 1% chance of catching a disease and so on.
Sleeping will help you recover your Immunity most of the time, however putting yourself to sleep with Sleeping Pills or Alcohol will prevent this recovery. Being well fed will also help you recover.
This variable is invisible to the player, as it is to a real person.
 
Severity:
When catching a disease, it will gradually rise in severity, before reaching a peak and lowering again in severity until the disease is gone. During this time, all you can do is treat symptoms and rest until you are better. There are 4 levels of Severity, based on when the disease's variable is at 1%-25%, 26%-50%, 51%-75% and 76%-100%.
Certain diseases, when treated with certain medications and the disease's variable reaches 0% will then be cured.
 
Nutrients:
There are many nutrients which a player will gain with a balanced diet. Lacking certain nutrients in your diet for too long will result in a Nutritional Disease. Nutritional Diseases bypass the immune system.
Calories:
Calories are the main weight determining nutrient. This value must be balanced with hunger consistently, or else obesity or anorexia may sneak up on the player.
Maximum: 3700
Minimum: -2200 Carbohydrates:
Carbohydrates are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Carbohydrates, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Lipids:
Lipids, previously called fats, are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Lipids, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Proteins:
Proteins are a determining factor in the increase and decrease of the Player's strength stat. Without the necessary proteins, the player will not be able to level up their strength. If a player consumes more than 400 Protein units, they will increase their strength in the same way as in the same manner as B40/B41. If the player consumes more than 700 Protein units, they will gain a 1.5 multiplier for strength increase. If a player's protein units falls below -250, they will start to lose strength, and reaching the minimum Protein units of -500 will result in the loss of strength with a multiplier of 2.
Maximum: 1000
Minimum: -500 Salts:
Salts can alter the rate at which a player becomes thirsty. This value is ignored unless the player has consumed more than 400 or 700 Salts resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Sugars:
Sugars are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Sugars, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Vitamins:
Vitamins are essential for keeping your Immune System strong. So long as the player consumes more than 400 Vitamins, their Immunity will recover as per normal while resting or sleeping. If the Sugar unit falls below 0, their Immunity will no longer recover.
Maximum: 500
Minimum: -500  
Diseases:
Diseases are visible in the Health tab when you have a certain level of First-Aid, but otherwise you'll have to guess by symptoms and circumstances.
Flu:
Sometimes, Zombies, Pigs (when added) or Chickens (when added) will spawn as infected with the Flu Virus. Being within 5 tiles from an infected zombie, the infected Zombie's corpse, an infected Player, an infected Player's corpse, an infected Pig or Chicken and an infected Pig or Chicken's corpse will make you vulnerable to catching the flu. Pigs and Chickens will also be at risk of catching it.
Symptoms are Congestion, Fever, Pain and a Sore Throat.
After catching Flu, there is a cooldown time before you can catch it again of around a month.
Severity 1:
The Flu is Asymptomatic at this severity, increasing the likelihood that you will spread it to other players unwittingly.
Severity 2:
Level 2 symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms, risk of death without treatment.
  Cold:
A cold is an ambient bacterial infection that can be caught when being wet, hot, cold or tired. Similar to Flu but far less severe but also far quicker to show symptoms.
Symptoms are Congestion, Fever and a Sore Throat.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Congestion and Sore Throat, no Fever.
Severity 2:
Level 2 Congestion and Sore Throat, no Fever.
Severity 3:
Level 3 Congestion and Sore Throat, Level 1 Fever.
Severity 4:
Level 4 Congestion and Sore Throat, Level 2 Fever.
  Pneumonia:
An ambient infection of the lungs that can be caught while Hypothermic. Similar to a Cold but far more severe.
Symptoms are Fever, Sore Throat and Shivers.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Sore Throat and Shivers, no Fever.
Severity  2:
Level 2 Sore Throat, Shivers and Fever.
Severity 3:
Level 3 Sore Throat, Shivers and Fever.
Severity 4
Level 4 Sore Throat, Shivers and Fever. Risk of death without treatment.
  Hayfever:
Can be caught by moving through dense vegetation during Spring.
Symptoms are Congestion and a Sore Throat.
Can be treated directly with Antihistamines.
Severity 1:
Level 1 Congestion, no sore throat.
Severity 2:
Level 2 Congestion, no Sore Throat.
Severity 3:
Level 3 Congestion, Level 1 Sore Throat.
Severity 4:
Level 4 Congestion, Level 2 Sore Throat.
  Stomach Flu:
An infection of the stomach lining, can be caught by eating uncooked or rotten food as well as drinking tainted water.
Symptoms are Nausea, Fever and Shivers.
Can be treated directly with Antibiotics.
Severity 1:
Level 1 Nausea, no Fever or Shivers.
Severity 2:
Level 2 Nausea, no Fever or Shivers.
Severity 3:
Level 3 Nausea, Fever and Shivers.
Severity 4:
Level 4 Nausea, Fever and Shivers. Risk of Death if untreated.
  Bleach Poisoning:
Bleach poisoning is a fast onset and fatal illness caused by directly drinking Bleach. It is always Severity 4.
Symptoms are Sore Throat, Pain, Anxiety, Shivers and gradual loss of Health.
Severity 4:
Level 4 Symptoms. Death is certain.
  Food Poisoning:
Food Poisoning is similar to Botulism but is caught by eating Poison Berries, Poison Mushrooms or food poisoned with Bleach.
Symptoms are Nausea, Sore Throat, Pain, Shivers and gradual loss of Health.
Severity 1:
Level 1 Nausea and Sore Throat, no others.
Severity 2:
Level 2 Nausea and Sore Throat, Level 1 Pain and Shivers. No loss of Health.
Severity 3:
Level 3 Nausea and Sore Throat, Level 2 Pain and Shivers. No loss of Health.
Severity 4:
Level 4 Nausea, Sore Throat, Pain, Shivers and a gradual Loss of Health. Can be fatal even with treatment if health already low.
  Rabies:
Caught by being Bitten by an infected animal. It is always Fatal if not treated with a Rabies Vaccine prior to Severity 2.
Symptoms are Anger, Stress, Weakness, Sore Throat, Agoraphobia, Pain when Drinking or Eating and Gradual Loss of Health.
Severity 1:
No symptoms.
Severity 2:
Level 2 Symptoms, but no loss of Health.
Severity 3:
Level 3 Symptoms, but no loss of Health.
Severity 4:
Level 4 symptoms and gradual loss of Health. Death is certain.
  Infection:
Caught by not properly treating a wound or spending a lot of time around corpses while your immune system is compromised.
Symptoms are Nausea, Pain, Shivers and Fever. If playing as a Hypochondriac, the symptoms are identical to Zombification if contracted from a Zombie Scratch instead but not always fatal.
Can be directly treated with Antibiotics or applying a sterilizing agent to the infected wound.
Severity 1:
Level 1 Nausea, no other symptoms.
Severity 2:
Level 2 Symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms. Can be fatal if left untreated.
  Scurvy:
Scurvy is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Vitamin intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Scurvy. Taking in the proper amount of Vitamins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Shivers, Pain and gradual loss of Health.
Can be directly treated with food rich in Vitamins or Vitamins medication.
Severity 1:
Level 1 Shivers and Pain, no loss of Health.
Severity 2:
Level 2 Shivers and Pain, no loss of Health.
Severity 3:
Level 3 Shivers and Pain, no loss of Health.
Severity 4:
Level 4 Shivers and Pain and the gradual loss of Health. Can be fatal if left untreated.
  Anemia:
Anemia is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Protein intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Anemia. Taking in the proper amount of Proteins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sleepiness, Weakness, Decreased Spatial Awareness, lowered item transfer rate and the gradual loss of Health.
Can be directly treated with food rich in Proteins.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Thyroditis:
Thyroditis is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Salt intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Thyroditis. Taking in the proper amount of Saltss will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sore Throat, Shivers and the gradual loss of Health.
Can be directly treated with food rich in Salts.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Zombification:
Caught by being Bitten or Scratched by a Zombie. It bypasses Immune system, with Bites always resulting in being infected and a 25% chance of being infected by a Scratch.
Symptoms are Stress, Sadness, Nausea, Untreatable Fever and the eventual death and rising as a Zombie.
Severity 1:
Level 1 Stress, no other Symptoms.
Severity 2:
Level 2 Stress, Level 1 Sadness, no other Symptoms.
Severity 3:
Level 3 Stress, Nausea, Sadness and Fever.
Severity 4:
Level 4 Stress, Nausea, Sadness and Fever. Death is certain.  
Abilities:
Players with high First-Aid or medical related Occupations/Traits will be able to deduce illnesses and administer medication directly to another Player, so Doctors and Nurses will have even more use in Multiplayer.
 
And that's that! Did I miss anything? What did y'all think?

Right now, the way disease is handled contrasts starkly with the overall complexity of the game...

My suggestion is to remove the ambiguity and turn certain Moodles into Symptoms, rather than have them as the disease themselves.
 
Symptoms:
Congestion:
Congestion replaces the Cold Moodle, becoming a symptom. It functions near identically, giving the player a chance to sneeze loudly, attracting zombies. Can be aided with an equipped tissue and treated with Antihistamines.
"Runny Nose"
"The sniffles"
"Congested"
"Severe Congestion" Fever:
Fever replaces the current Sick Moodle, becoming a symptom. Each stage will increase your character's temperature by a certain amount and will cause damage on its' highest level while also lowering healing, strength and increasing the rate at which a player gets sleepy. Can be treated with Antipyretics unless it is a symptom of Zombification. Equipping a Cold Pack that has been cooled in a freezer or a bag of Frozen Peas can also help.
"Bit of a Temperature"
"Temperature"
"Severe Temperature"
"Terminal Fever" Nausea:
Nausea is the other half of the current Sick Moodle becoming a symptom in its' own right. It lowers healing, strength and speed. It can be treated with Antiemetics.
"Bit Sick"
"Sick"
"Really Sick"
"Severe Nausea" Sore Throat:
A Sore Throat is similar to Congestion, but may cause pain when eating with an increasing chance to loudly cough which may attract nearby zombies. Can be treated with Cough Syrup.
"Scratchy Throat"
"Painful Throat"
"Rough Cough"
"Severe Coughing" Shivers:
Shivering which will lower the accuracy of the player. Can be relieved with Painkillers.
"A bit Shaky"
"Shaky"
"Shivering"
"Severe Shivering"  
While those are direct symptoms, other Moodles such as Pain would also be symptoms, directly or indirectly.

Medications:
Painkillers:
Relieves Pain and Shivers. Can cause Nausea if abused. Beta Blockers:
Relieves Panic. Antidepressants:
Relieves Sadness. Can cause Anger if abused. Sleeping Tablets:
Helps you sleep. Can cause Nausea or loss of Health if abused or taken while Drunk. Vitamins:
These should boost healing and help you recover some Immunity. Antibiotics:
Speeds up healing of Colds, Pneumonia, Infection and Stomach Flu. Can cause Nausea if abused. Caffeine Pills:
Relieves Sleepiness. Can cause Shivers if abused. Antihistamines:
Relieves Congestion. Can cause Sleepiness if abused. Antipyretics:
Relieves a traditional Fever. Can cause Nausea if abused. Antiemetics:
Relieves Nausea. Cough Syrup:
Relieves a Sore Throat, may also make you Drunk if taken in large quantities. Flu Vaccine Vial:
A vial containing a Vaccine for the Flu Virus. Can be added to a syringe so that you can administer a Flu Shot. Each Vial can fill a Syringe 4 times. Taking a Flu Shot will cause the Severity of Flu to begin to decline and will provide you with a month of immunity to the Flu Virus. Common Infection Vaccine Vial:
A vial containing a Vaccine for the Infection. Can be added to a syringe so that you can administer a Common Infection Shot. Each Vial can fill a Syringe 4 times. Taking a Common Infection Shot will cause the Severity of a Common Infection to decline and will provide you with a month of immunity to the Common Infection. Rabies Vaccine:
A vial containing a Vaccine for the Rabies Virus. Can be added to a syringe so that you can administer a Rabies Shot. Each Vial Can fill a Syringe 4 times. Taking a Common Infection Shot will cure Rabies, provided you take it prior to the manifestation of symptoms, and will provide you with a month of immunity to the Rabies Virus.  
There are a few others I'd like such as Morphine and so on that would have a chance to cause addiction, but the ones I've added are more to expand on what is present, rather than add too much new.
 
Items:
Pill Dispenser:
A container with random pills inside. Water bottle with Dissolved Painkiller:
As the name suggests. The Player can dissolve up to 4 units of Painkillers into a Water Bottle, allowing for Painkiller use to be stretched out, if a bit weakened. Surgical Mask:
Surgical Masks (along with gasmasks) provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, as long as they are at least 50% clean with no damage. Hazmat Gear:
A full set of Hazmat Gear will provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, so long as they are undamaged. Syringe:
A medical syringe used for injecting yourself with a Vaccine. Maybe also for Addictive Drugs. Empty Vial:
Garbage item left over when adding a Vaccine to a Syringe. Can hold water.  
Traits:
Strong Immune System:
Chance of catching a disease is halved. Can go well with Iron Gut and Outdoorsman for a Robust Genetics build. Weak Immune System:
Replaces Prone To Illness. Chance of catching a disease is doubled, more likely for a wound to be infected and faster Zombification. Iron Gut:
Chance of catching Stomach Flu from food or water is halved. Weak Stomach:
Chance of catching Stomach Flu doubled. Outdoorsman:
Being wet does not weaken your Immune System. Immune to Hayfever. Allergy Prone:
Very prone to Hayfever. Hayfever gained this way bypasses Immune System Variable with there always being a 10% chance of contracting Hayfever when moving through thick Vegetation in off seasons and a 25% chance in Spring. Resilient:
Less likely for wounds to become infected and slows Zombification. Asthmatic:
40% increase in running endurance loss, 30% increase in swing endurance lost and a chance to loudly cough when Exerted. Hypochondriac:
May develop infection symptoms without being infected. Easily Amused:
Slower rate of boredom and unhappiness. Depression:
Becomes bored faster and gradually becomes sadder with time.  
The Immune System:
The Immune System, or simply just the Immunity variable, determines the chance of becoming ill.
At 0%, you are fully healthy and won't get sick.
But any activity while Sick, Dirty, Bloody, Wet, Sleepy, Exerted, Sad, Injured or Hungry will cause it to gradually rise. At 1%, you have a 1% chance of catching a disease and so on.
Sleeping will help you recover your Immunity most of the time, however putting yourself to sleep with Sleeping Pills or Alcohol will prevent this recovery. Being well fed will also help you recover.
This variable is invisible to the player, as it is to a real person.
 
Severity:
When catching a disease, it will gradually rise in severity, before reaching a peak and lowering again in severity until the disease is gone. During this time, all you can do is treat symptoms and rest until you are better. There are 4 levels of Severity, based on when the disease's variable is at 1%-25%, 26%-50%, 51%-75% and 76%-100%.
Certain diseases, when treated with certain medications and the disease's variable reaches 0% will then be cured.
 
Nutrients:
There are many nutrients which a player will gain with a balanced diet. Lacking certain nutrients in your diet for too long will result in a Nutritional Disease. Nutritional Diseases bypass the immune system.
Calories:
Calories are the main weight determining nutrient. This value must be balanced with hunger consistently, or else obesity or anorexia may sneak up on the player.
Maximum: 3700
Minimum: -2200 Carbohydrates:
Carbohydrates are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Carbohydrates, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Lipids:
Lipids, previously called fats, are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Lipids, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Proteins:
Proteins are a determining factor in the increase and decrease of the Player's strength stat. Without the necessary proteins, the player will not be able to level up their strength. If a player consumes more than 400 Protein units, they will increase their strength in the same way as in the same manner as B40/B41. If the player consumes more than 700 Protein units, they will gain a 1.5 multiplier for strength increase. If a player's protein units falls below -250, they will start to lose strength, and reaching the minimum Protein units of -500 will result in the loss of strength with a multiplier of 2.
Maximum: 1000
Minimum: -500 Salts:
Salts can alter the rate at which a player becomes thirsty. This value is ignored unless the player has consumed more than 400 or 700 Salts resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Sugars:
Sugars are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Sugars, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Vitamins:
Vitamins are essential for keeping your Immune System strong. So long as the player consumes more than 400 Vitamins, their Immunity will recover as per normal while resting or sleeping. If the Sugar unit falls below 0, their Immunity will no longer recover.
Maximum: 500
Minimum: -500  
Diseases:
Diseases are visible in the Health tab when you have a certain level of First-Aid, but otherwise you'll have to guess by symptoms and circumstances.
Flu:
Sometimes, Zombies, Pigs (when added) or Chickens (when added) will spawn as infected with the Flu Virus. Being within 5 tiles from an infected zombie, the infected Zombie's corpse, an infected Player, an infected Player's corpse, an infected Pig or Chicken and an infected Pig or Chicken's corpse will make you vulnerable to catching the flu. Pigs and Chickens will also be at risk of catching it.
Symptoms are Congestion, Fever, Pain and a Sore Throat.
After catching Flu, there is a cooldown time before you can catch it again of around a month.
Severity 1:
The Flu is Asymptomatic at this severity, increasing the likelihood that you will spread it to other players unwittingly.
Severity 2:
Level 2 symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms, risk of death without treatment.
  Cold:
A cold is an ambient bacterial infection that can be caught when being wet, hot, cold or tired. Similar to Flu but far less severe but also far quicker to show symptoms.
Symptoms are Congestion, Fever and a Sore Throat.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Congestion and Sore Throat, no Fever.
Severity 2:
Level 2 Congestion and Sore Throat, no Fever.
Severity 3:
Level 3 Congestion and Sore Throat, Level 1 Fever.
Severity 4:
Level 4 Congestion and Sore Throat, Level 2 Fever.
  Pneumonia:
An ambient infection of the lungs that can be caught while Hypothermic. Similar to a Cold but far more severe.
Symptoms are Fever, Sore Throat and Shivers.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Sore Throat and Shivers, no Fever.
Severity  2:
Level 2 Sore Throat, Shivers and Fever.
Severity 3:
Level 3 Sore Throat, Shivers and Fever.
Severity 4
Level 4 Sore Throat, Shivers and Fever. Risk of death without treatment.
  Hayfever:
Can be caught by moving through dense vegetation during Spring.
Symptoms are Congestion and a Sore Throat.
Can be treated directly with Antihistamines.
Severity 1:
Level 1 Congestion, no sore throat.
Severity 2:
Level 2 Congestion, no Sore Throat.
Severity 3:
Level 3 Congestion, Level 1 Sore Throat.
Severity 4:
Level 4 Congestion, Level 2 Sore Throat.
  Stomach Flu:
An infection of the stomach lining, can be caught by eating uncooked or rotten food as well as drinking tainted water.
Symptoms are Nausea, Fever and Shivers.
Can be treated directly with Antibiotics.
Severity 1:
Level 1 Nausea, no Fever or Shivers.
Severity 2:
Level 2 Nausea, no Fever or Shivers.
Severity 3:
Level 3 Nausea, Fever and Shivers.
Severity 4:
Level 4 Nausea, Fever and Shivers. Risk of Death if untreated.
  Bleach Poisoning:
Bleach poisoning is a fast onset and fatal illness caused by directly drinking Bleach. It is always Severity 4.
Symptoms are Sore Throat, Pain, Anxiety, Shivers and gradual loss of Health.
Severity 4:
Level 4 Symptoms. Death is certain.
  Food Poisoning:
Food Poisoning is similar to Botulism but is caught by eating Poison Berries, Poison Mushrooms or food poisoned with Bleach.
Symptoms are Nausea, Sore Throat, Pain, Shivers and gradual loss of Health.
Severity 1:
Level 1 Nausea and Sore Throat, no others.
Severity 2:
Level 2 Nausea and Sore Throat, Level 1 Pain and Shivers. No loss of Health.
Severity 3:
Level 3 Nausea and Sore Throat, Level 2 Pain and Shivers. No loss of Health.
Severity 4:
Level 4 Nausea, Sore Throat, Pain, Shivers and a gradual Loss of Health. Can be fatal even with treatment if health already low.
  Rabies:
Caught by being Bitten by an infected animal. It is always Fatal if not treated with a Rabies Vaccine prior to Severity 2.
Symptoms are Anger, Stress, Weakness, Sore Throat, Agoraphobia, Pain when Drinking or Eating and Gradual Loss of Health.
Severity 1:
No symptoms.
Severity 2:
Level 2 Symptoms, but no loss of Health.
Severity 3:
Level 3 Symptoms, but no loss of Health.
Severity 4:
Level 4 symptoms and gradual loss of Health. Death is certain.
  Infection:
Caught by not properly treating a wound or spending a lot of time around corpses while your immune system is compromised.
Symptoms are Nausea, Pain, Shivers and Fever. If playing as a Hypochondriac, the symptoms are identical to Zombification if contracted from a Zombie Scratch instead but not always fatal.
Can be directly treated with Antibiotics or applying a sterilizing agent to the infected wound.
Severity 1:
Level 1 Nausea, no other symptoms.
Severity 2:
Level 2 Symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms. Can be fatal if left untreated.
  Scurvy:
Scurvy is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Vitamin intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Scurvy. Taking in the proper amount of Vitamins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Shivers, Pain and gradual loss of Health.
Can be directly treated with food rich in Vitamins or Vitamins medication.
Severity 1:
Level 1 Shivers and Pain, no loss of Health.
Severity 2:
Level 2 Shivers and Pain, no loss of Health.
Severity 3:
Level 3 Shivers and Pain, no loss of Health.
Severity 4:
Level 4 Shivers and Pain and the gradual loss of Health. Can be fatal if left untreated.
  Anemia:
Anemia is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Protein intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Anemia. Taking in the proper amount of Proteins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sleepiness, Weakness, Decreased Spatial Awareness, lowered item transfer rate and the gradual loss of Health.
Can be directly treated with food rich in Proteins.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Thyroditis:
Thyroditis is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Salt intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Thyroditis. Taking in the proper amount of Saltss will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sore Throat, Shivers and the gradual loss of Health.
Can be directly treated with food rich in Salts.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Zombification:
Caught by being Bitten or Scratched by a Zombie. It bypasses Immune system, with Bites always resulting in being infected and a 25% chance of being infected by a Scratch.
Symptoms are Stress, Sadness, Nausea, Untreatable Fever and the eventual death and rising as a Zombie.
Severity 1:
Level 1 Stress, no other Symptoms.
Severity 2:
Level 2 Stress, Level 1 Sadness, no other Symptoms.
Severity 3:
Level 3 Stress, Nausea, Sadness and Fever.
Severity 4:
Level 4 Stress, Nausea, Sadness and Fever. Death is certain.  
Abilities:
Players with high First-Aid or medical related Occupations/Traits will be able to deduce illnesses and administer medication directly to another Player, so Doctors and Nurses will have even more use in Multiplayer.
 
And that's that! Did I miss anything? What did y'all think?

Right now, the way disease is handled contrasts starkly with the overall complexity of the game...

My suggestion is to remove the ambiguity and turn certain Moodles into Symptoms, rather than have them as the disease themselves.
 
Symptoms:
Congestion:
Congestion replaces the Cold Moodle, becoming a symptom. It functions near identically, giving the player a chance to sneeze loudly, attracting zombies. Can be aided with an equipped tissue and treated with Antihistamines.
"Runny Nose"
"The sniffles"
"Congested"
"Severe Congestion" Fever:
Fever replaces the current Sick Moodle, becoming a symptom. Each stage will increase your character's temperature by a certain amount and will cause damage on its' highest level while also lowering healing, strength and increasing the rate at which a player gets sleepy. Can be treated with Antipyretics unless it is a symptom of Zombification. Equipping a Cold Pack that has been cooled in a freezer or a bag of Frozen Peas can also help.
"Bit of a Temperature"
"Temperature"
"Severe Temperature"
"Terminal Fever" Nausea:
Nausea is the other half of the current Sick Moodle becoming a symptom in its' own right. It lowers healing, strength and speed. It can be treated with Antiemetics.
"Bit Sick"
"Sick"
"Really Sick"
"Severe Nausea" Sore Throat:
A Sore Throat is similar to Congestion, but may cause pain when eating with an increasing chance to loudly cough which may attract nearby zombies. Can be treated with Cough Syrup.
"Scratchy Throat"
"Painful Throat"
"Rough Cough"
"Severe Coughing" Shivers:
Shivering which will lower the accuracy of the player. Can be relieved with Painkillers.
"A bit Shaky"
"Shaky"
"Shivering"
"Severe Shivering"  
While those are direct symptoms, other Moodles such as Pain would also be symptoms, directly or indirectly.

Medications:
Painkillers:
Relieves Pain and Shivers. Can cause Nausea if abused. Beta Blockers:
Relieves Panic. Antidepressants:
Relieves Sadness. Can cause Anger if abused. Sleeping Tablets:
Helps you sleep. Can cause Nausea or loss of Health if abused or taken while Drunk. Vitamins:
These should boost healing and help you recover some Immunity. Antibiotics:
Speeds up healing of Colds, Pneumonia, Infection and Stomach Flu. Can cause Nausea if abused. Caffeine Pills:
Relieves Sleepiness. Can cause Shivers if abused. Antihistamines:
Relieves Congestion. Can cause Sleepiness if abused. Antipyretics:
Relieves a traditional Fever. Can cause Nausea if abused. Antiemetics:
Relieves Nausea. Cough Syrup:
Relieves a Sore Throat, may also make you Drunk if taken in large quantities. Flu Vaccine Vial:
A vial containing a Vaccine for the Flu Virus. Can be added to a syringe so that you can administer a Flu Shot. Each Vial can fill a Syringe 4 times. Taking a Flu Shot will cause the Severity of Flu to begin to decline and will provide you with a month of immunity to the Flu Virus. Common Infection Vaccine Vial:
A vial containing a Vaccine for the Infection. Can be added to a syringe so that you can administer a Common Infection Shot. Each Vial can fill a Syringe 4 times. Taking a Common Infection Shot will cause the Severity of a Common Infection to decline and will provide you with a month of immunity to the Common Infection. Rabies Vaccine:
A vial containing a Vaccine for the Rabies Virus. Can be added to a syringe so that you can administer a Rabies Shot. Each Vial Can fill a Syringe 4 times. Taking a Common Infection Shot will cure Rabies, provided you take it prior to the manifestation of symptoms, and will provide you with a month of immunity to the Rabies Virus.  
There are a few others I'd like such as Morphine and so on that would have a chance to cause addiction, but the ones I've added are more to expand on what is present, rather than add too much new.
 
Items:
Pill Dispenser:
A container with random pills inside. Water bottle with Dissolved Painkiller:
As the name suggests. The Player can dissolve up to 4 units of Painkillers into a Water Bottle, allowing for Painkiller use to be stretched out, if a bit weakened. Surgical Mask:
Surgical Masks (along with gasmasks) provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, as long as they are at least 50% clean with no damage. Hazmat Gear:
A full set of Hazmat Gear will provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, so long as they are undamaged. Syringe:
A medical syringe used for injecting yourself with a Vaccine. Maybe also for Addictive Drugs. Empty Vial:
Garbage item left over when adding a Vaccine to a Syringe. Can hold water.  
Traits:
Strong Immune System:
Chance of catching a disease is halved. Can go well with Iron Gut and Outdoorsman for a Robust Genetics build. Weak Immune System:
Replaces Prone To Illness. Chance of catching a disease is doubled, more likely for a wound to be infected and faster Zombification. Iron Gut:
Chance of catching Stomach Flu from food or water is halved. Weak Stomach:
Chance of catching Stomach Flu doubled. Outdoorsman:
Being wet does not weaken your Immune System. Immune to Hayfever. Allergy Prone:
Very prone to Hayfever. Hayfever gained this way bypasses Immune System Variable with there always being a 10% chance of contracting Hayfever when moving through thick Vegetation in off seasons and a 25% chance in Spring. Resilient:
Less likely for wounds to become infected and slows Zombification. Asthmatic:
40% increase in running endurance loss, 30% increase in swing endurance lost and a chance to loudly cough when Exerted. Hypochondriac:
May develop infection symptoms without being infected. Easily Amused:
Slower rate of boredom and unhappiness. Depression:
Becomes bored faster and gradually becomes sadder with time.  
The Immune System:
The Immune System, or simply just the Immunity variable, determines the chance of becoming ill.
At 0%, you are fully healthy and won't get sick.
But any activity while Sick, Dirty, Bloody, Wet, Sleepy, Exerted, Sad, Injured or Hungry will cause it to gradually rise. At 1%, you have a 1% chance of catching a disease and so on.
Sleeping will help you recover your Immunity most of the time, however putting yourself to sleep with Sleeping Pills or Alcohol will prevent this recovery. Being well fed will also help you recover.
This variable is invisible to the player, as it is to a real person.
 
Severity:
When catching a disease, it will gradually rise in severity, before reaching a peak and lowering again in severity until the disease is gone. During this time, all you can do is treat symptoms and rest until you are better. There are 4 levels of Severity, based on when the disease's variable is at 1%-25%, 26%-50%, 51%-75% and 76%-100%.
Certain diseases, when treated with certain medications and the disease's variable reaches 0% will then be cured.
 
Nutrients:
There are many nutrients which a player will gain with a balanced diet. Lacking certain nutrients in your diet for too long will result in a Nutritional Disease. Nutritional Diseases bypass the immune system.
Calories:
Calories are the main weight determining nutrient. This value must be balanced with hunger consistently, or else obesity or anorexia may sneak up on the player.
Maximum: 3700
Minimum: -2200 Carbohydrates:
Carbohydrates are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Carbohydrates, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Lipids:
Lipids, previously called fats, are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Lipids, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Proteins:
Proteins are a determining factor in the increase and decrease of the Player's strength stat. Without the necessary proteins, the player will not be able to level up their strength. If a player consumes more than 400 Protein units, they will increase their strength in the same way as in the same manner as B40/B41. If the player consumes more than 700 Protein units, they will gain a 1.5 multiplier for strength increase. If a player's protein units falls below -250, they will start to lose strength, and reaching the minimum Protein units of -500 will result in the loss of strength with a multiplier of 2.
Maximum: 1000
Minimum: -500 Salts:
Salts can alter the rate at which a player becomes thirsty. This value is ignored unless the player has consumed more than 400 or 700 Salts resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Sugars:
Sugars are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Sugars, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Vitamins:
Vitamins are essential for keeping your Immune System strong. So long as the player consumes more than 400 Vitamins, their Immunity will recover as per normal while resting or sleeping. If the Sugar unit falls below 0, their Immunity will no longer recover.
Maximum: 500
Minimum: -500  
Diseases:
Diseases are visible in the Health tab when you have a certain level of First-Aid, but otherwise you'll have to guess by symptoms and circumstances.
Flu:
Sometimes, Zombies, Pigs (when added) or Chickens (when added) will spawn as infected with the Flu Virus. Being within 5 tiles from an infected zombie, the infected Zombie's corpse, an infected Player, an infected Player's corpse, an infected Pig or Chicken and an infected Pig or Chicken's corpse will make you vulnerable to catching the flu. Pigs and Chickens will also be at risk of catching it.
Symptoms are Congestion, Fever, Pain and a Sore Throat.
After catching Flu, there is a cooldown time before you can catch it again of around a month.
Severity 1:
The Flu is Asymptomatic at this severity, increasing the likelihood that you will spread it to other players unwittingly.
Severity 2:
Level 2 symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms, risk of death without treatment.
  Cold:
A cold is an ambient bacterial infection that can be caught when being wet, hot, cold or tired. Similar to Flu but far less severe but also far quicker to show symptoms.
Symptoms are Congestion, Fever and a Sore Throat.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Congestion and Sore Throat, no Fever.
Severity 2:
Level 2 Congestion and Sore Throat, no Fever.
Severity 3:
Level 3 Congestion and Sore Throat, Level 1 Fever.
Severity 4:
Level 4 Congestion and Sore Throat, Level 2 Fever.
  Pneumonia:
An ambient infection of the lungs that can be caught while Hypothermic. Similar to a Cold but far more severe.
Symptoms are Fever, Sore Throat and Shivers.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Sore Throat and Shivers, no Fever.
Severity  2:
Level 2 Sore Throat, Shivers and Fever.
Severity 3:
Level 3 Sore Throat, Shivers and Fever.
Severity 4
Level 4 Sore Throat, Shivers and Fever. Risk of death without treatment.
  Hayfever:
Can be caught by moving through dense vegetation during Spring.
Symptoms are Congestion and a Sore Throat.
Can be treated directly with Antihistamines.
Severity 1:
Level 1 Congestion, no sore throat.
Severity 2:
Level 2 Congestion, no Sore Throat.
Severity 3:
Level 3 Congestion, Level 1 Sore Throat.
Severity 4:
Level 4 Congestion, Level 2 Sore Throat.
  Stomach Flu:
An infection of the stomach lining, can be caught by eating uncooked or rotten food as well as drinking tainted water.
Symptoms are Nausea, Fever and Shivers.
Can be treated directly with Antibiotics.
Severity 1:
Level 1 Nausea, no Fever or Shivers.
Severity 2:
Level 2 Nausea, no Fever or Shivers.
Severity 3:
Level 3 Nausea, Fever and Shivers.
Severity 4:
Level 4 Nausea, Fever and Shivers. Risk of Death if untreated.
  Bleach Poisoning:
Bleach poisoning is a fast onset and fatal illness caused by directly drinking Bleach. It is always Severity 4.
Symptoms are Sore Throat, Pain, Anxiety, Shivers and gradual loss of Health.
Severity 4:
Level 4 Symptoms. Death is certain.
  Food Poisoning:
Food Poisoning is similar to Botulism but is caught by eating Poison Berries, Poison Mushrooms or food poisoned with Bleach.
Symptoms are Nausea, Sore Throat, Pain, Shivers and gradual loss of Health.
Severity 1:
Level 1 Nausea and Sore Throat, no others.
Severity 2:
Level 2 Nausea and Sore Throat, Level 1 Pain and Shivers. No loss of Health.
Severity 3:
Level 3 Nausea and Sore Throat, Level 2 Pain and Shivers. No loss of Health.
Severity 4:
Level 4 Nausea, Sore Throat, Pain, Shivers and a gradual Loss of Health. Can be fatal even with treatment if health already low.
  Rabies:
Caught by being Bitten by an infected animal. It is always Fatal if not treated with a Rabies Vaccine prior to Severity 2.
Symptoms are Anger, Stress, Weakness, Sore Throat, Agoraphobia, Pain when Drinking or Eating and Gradual Loss of Health.
Severity 1:
No symptoms.
Severity 2:
Level 2 Symptoms, but no loss of Health.
Severity 3:
Level 3 Symptoms, but no loss of Health.
Severity 4:
Level 4 symptoms and gradual loss of Health. Death is certain.
  Infection:
Caught by not properly treating a wound or spending a lot of time around corpses while your immune system is compromised.
Symptoms are Nausea, Pain, Shivers and Fever. If playing as a Hypochondriac, the symptoms are identical to Zombification if contracted from a Zombie Scratch instead but not always fatal.
Can be directly treated with Antibiotics or applying a sterilizing agent to the infected wound.
Severity 1:
Level 1 Nausea, no other symptoms.
Severity 2:
Level 2 Symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms. Can be fatal if left untreated.
  Scurvy:
Scurvy is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Vitamin intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Scurvy. Taking in the proper amount of Vitamins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Shivers, Pain and gradual loss of Health.
Can be directly treated with food rich in Vitamins or Vitamins medication.
Severity 1:
Level 1 Shivers and Pain, no loss of Health.
Severity 2:
Level 2 Shivers and Pain, no loss of Health.
Severity 3:
Level 3 Shivers and Pain, no loss of Health.
Severity 4:
Level 4 Shivers and Pain and the gradual loss of Health. Can be fatal if left untreated.
  Anemia:
Anemia is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Protein intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Anemia. Taking in the proper amount of Proteins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sleepiness, Weakness, Decreased Spatial Awareness, lowered item transfer rate and the gradual loss of Health.
Can be directly treated with food rich in Proteins.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Thyroditis:
Thyroditis is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Salt intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Thyroditis. Taking in the proper amount of Saltss will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sore Throat, Shivers and the gradual loss of Health.
Can be directly treated with food rich in Salts.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Zombification:
Caught by being Bitten or Scratched by a Zombie. It bypasses Immune system, with Bites always resulting in being infected and a 25% chance of being infected by a Scratch.
Symptoms are Stress, Sadness, Nausea, Untreatable Fever and the eventual death and rising as a Zombie.
Severity 1:
Level 1 Stress, no other Symptoms.
Severity 2:
Level 2 Stress, Level 1 Sadness, no other Symptoms.
Severity 3:
Level 3 Stress, Nausea, Sadness and Fever.
Severity 4:
Level 4 Stress, Nausea, Sadness and Fever. Death is certain.  
Abilities:
Players with high First-Aid or medical related Occupations/Traits will be able to deduce illnesses and administer medication directly to another Player, so Doctors and Nurses will have even more use in Multiplayer.
 
And that's that! Did I miss anything? What did y'all think?

Right now, the way disease is handled contrasts starkly with the overall complexity of the game...

My suggestion is to remove the ambiguity and turn certain Moodles into Symptoms, rather than have them as the disease themselves.
 
Symptoms:
Congestion:
Congestion replaces the Cold Moodle, becoming a symptom. It functions near identically, giving the player a chance to sneeze loudly, attracting zombies. Can be aided with an equipped tissue and treated with Antihistamines.
"Runny Nose"
"The sniffles"
"Congested"
"Severe Congestion" Fever:
Fever replaces the current Sick Moodle, becoming a symptom. Each stage will increase your character's temperature by a certain amount and will cause damage on its' highest level while also lowering healing, strength and increasing the rate at which a player gets sleepy. Can be treated with Antipyretics unless it is a symptom of Zombification. Equipping a Cold Pack that has been cooled in a freezer or a bag of Frozen Peas can also help.
"Bit of a Temperature"
"Temperature"
"Severe Temperature"
"Terminal Fever" Nausea:
Nausea is the other half of the current Sick Moodle becoming a symptom in its' own right. It lowers healing, strength and speed. It can be treated with Antiemetics.
"Bit Sick"
"Sick"
"Really Sick"
"Severe Nausea" Sore Throat:
A Sore Throat is similar to Congestion, but may cause pain when eating with an increasing chance to loudly cough which may attract nearby zombies. Can be treated with Cough Syrup.
"Scratchy Throat"
"Painful Throat"
"Rough Cough"
"Severe Coughing" Shivers:
Shivering which will lower the accuracy of the player. Can be relieved with Painkillers.
"A bit Shaky"
"Shaky"
"Shivering"
"Severe Shivering"  
While those are direct symptoms, other Moodles such as Pain would also be symptoms, directly or indirectly.

Medications:
Painkillers:
Relieves Pain and Shivers. Can cause Nausea if abused. Beta Blockers:
Relieves Panic. Antidepressants:
Relieves Sadness. Can cause Anger if abused. Sleeping Tablets:
Helps you sleep. Can cause Nausea or loss of Health if abused or taken while Drunk. Vitamins:
These should boost healing and help you recover some Immunity. Antibiotics:
Speeds up healing of Colds, Pneumonia, Infection and Stomach Flu. Can cause Nausea if abused. Caffeine Pills:
Relieves Sleepiness. Can cause Shivers if abused. Antihistamines:
Relieves Congestion. Can cause Sleepiness if abused. Antipyretics:
Relieves a traditional Fever. Can cause Nausea if abused. Antiemetics:
Relieves Nausea. Cough Syrup:
Relieves a Sore Throat, may also make you Drunk if taken in large quantities. Flu Vaccine Vial:
A vial containing a Vaccine for the Flu Virus. Can be added to a syringe so that you can administer a Flu Shot. Each Vial can fill a Syringe 4 times. Taking a Flu Shot will cause the Severity of Flu to begin to decline and will provide you with a month of immunity to the Flu Virus. Common Infection Vaccine Vial:
A vial containing a Vaccine for the Infection. Can be added to a syringe so that you can administer a Common Infection Shot. Each Vial can fill a Syringe 4 times. Taking a Common Infection Shot will cause the Severity of a Common Infection to decline and will provide you with a month of immunity to the Common Infection. Rabies Vaccine:
A vial containing a Vaccine for the Rabies Virus. Can be added to a syringe so that you can administer a Rabies Shot. Each Vial Can fill a Syringe 4 times. Taking a Common Infection Shot will cure Rabies, provided you take it prior to the manifestation of symptoms, and will provide you with a month of immunity to the Rabies Virus.  
There are a few others I'd like such as Morphine and so on that would have a chance to cause addiction, but the ones I've added are more to expand on what is present, rather than add too much new.
 
Items:
Pill Dispenser:
A container with random pills inside. Water bottle with Dissolved Painkiller:
As the name suggests. The Player can dissolve up to 4 units of Painkillers into a Water Bottle, allowing for Painkiller use to be stretched out, if a bit weakened. Surgical Mask:
Surgical Masks (along with gasmasks) provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, as long as they are at least 50% clean with no damage. Hazmat Gear:
A full set of Hazmat Gear will provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, so long as they are undamaged. Syringe:
A medical syringe used for injecting yourself with a Vaccine. Maybe also for Addictive Drugs. Empty Vial:
Garbage item left over when adding a Vaccine to a Syringe. Can hold water.  
Traits:
Strong Immune System:
Chance of catching a disease is halved. Can go well with Iron Gut and Outdoorsman for a Robust Genetics build. Weak Immune System:
Replaces Prone To Illness. Chance of catching a disease is doubled, more likely for a wound to be infected and faster Zombification. Iron Gut:
Chance of catching Stomach Flu from food or water is halved. Weak Stomach:
Chance of catching Stomach Flu doubled. Outdoorsman:
Being wet does not weaken your Immune System. Immune to Hayfever. Allergy Prone:
Very prone to Hayfever. Hayfever gained this way bypasses Immune System Variable with there always being a 10% chance of contracting Hayfever when moving through thick Vegetation in off seasons and a 25% chance in Spring. Resilient:
Less likely for wounds to become infected and slows Zombification. Asthmatic:
40% increase in running endurance loss, 30% increase in swing endurance lost and a chance to loudly cough when Exerted. Hypochondriac:
May develop infection symptoms without being infected. Easily Amused:
Slower rate of boredom and unhappiness. Depression:
Becomes bored faster and gradually becomes sadder with time.  
The Immune System:
The Immune System, or simply just the Immunity variable, determines the chance of becoming ill.
At 0%, you are fully healthy and won't get sick.
But any activity while Sick, Dirty, Bloody, Wet, Sleepy, Exerted, Sad, Injured or Hungry will cause it to gradually rise. At 1%, you have a 1% chance of catching a disease and so on.
Sleeping will help you recover your Immunity most of the time, however putting yourself to sleep with Sleeping Pills or Alcohol will prevent this recovery. Being well fed will also help you recover.
This variable is invisible to the player, as it is to a real person.
 
Severity:
When catching a disease, it will gradually rise in severity, before reaching a peak and lowering again in severity until the disease is gone. During this time, all you can do is treat symptoms and rest until you are better. There are 4 levels of Severity, based on when the disease's variable is at 1%-25%, 26%-50%, 51%-75% and 76%-100%.
Certain diseases, when treated with certain medications and the disease's variable reaches 0% will then be cured.
 
Nutrients:
There are many nutrients which a player will gain with a balanced diet. Lacking certain nutrients in your diet for too long will result in a Nutritional Disease. Nutritional Diseases bypass the immune system.
Calories:
Calories are the main weight determining nutrient. This value must be balanced with hunger consistently, or else obesity or anorexia may sneak up on the player.
Maximum: 3700
Minimum: -2200 Carbohydrates:
Carbohydrates are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Carbohydrates, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Lipids:
Lipids, previously called fats, are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Lipids, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Proteins:
Proteins are a determining factor in the increase and decrease of the Player's strength stat. Without the necessary proteins, the player will not be able to level up their strength. If a player consumes more than 400 Protein units, they will increase their strength in the same way as in the same manner as B40/B41. If the player consumes more than 700 Protein units, they will gain a 1.5 multiplier for strength increase. If a player's protein units falls below -250, they will start to lose strength, and reaching the minimum Protein units of -500 will result in the loss of strength with a multiplier of 2.
Maximum: 1000
Minimum: -500 Salts:
Salts can alter the rate at which a player becomes thirsty. This value is ignored unless the player has consumed more than 400 or 700 Salts resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Sugars:
Sugars are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Sugars, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Vitamins:
Vitamins are essential for keeping your Immune System strong. So long as the player consumes more than 400 Vitamins, their Immunity will recover as per normal while resting or sleeping. If the Sugar unit falls below 0, their Immunity will no longer recover.
Maximum: 500
Minimum: -500  
Diseases:
Diseases are visible in the Health tab when you have a certain level of First-Aid, but otherwise you'll have to guess by symptoms and circumstances.
Flu:
Sometimes, Zombies, Pigs (when added) or Chickens (when added) will spawn as infected with the Flu Virus. Being within 5 tiles from an infected zombie, the infected Zombie's corpse, an infected Player, an infected Player's corpse, an infected Pig or Chicken and an infected Pig or Chicken's corpse will make you vulnerable to catching the flu. Pigs and Chickens will also be at risk of catching it.
Symptoms are Congestion, Fever, Pain and a Sore Throat.
After catching Flu, there is a cooldown time before you can catch it again of around a month.
Severity 1:
The Flu is Asymptomatic at this severity, increasing the likelihood that you will spread it to other players unwittingly.
Severity 2:
Level 2 symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms, risk of death without treatment.
  Cold:
A cold is an ambient bacterial infection that can be caught when being wet, hot, cold or tired. Similar to Flu but far less severe but also far quicker to show symptoms.
Symptoms are Congestion, Fever and a Sore Throat.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Congestion and Sore Throat, no Fever.
Severity 2:
Level 2 Congestion and Sore Throat, no Fever.
Severity 3:
Level 3 Congestion and Sore Throat, Level 1 Fever.
Severity 4:
Level 4 Congestion and Sore Throat, Level 2 Fever.
  Pneumonia:
An ambient infection of the lungs that can be caught while Hypothermic. Similar to a Cold but far more severe.
Symptoms are Fever, Sore Throat and Shivers.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Sore Throat and Shivers, no Fever.
Severity  2:
Level 2 Sore Throat, Shivers and Fever.
Severity 3:
Level 3 Sore Throat, Shivers and Fever.
Severity 4
Level 4 Sore Throat, Shivers and Fever. Risk of death without treatment.
  Hayfever:
Can be caught by moving through dense vegetation during Spring.
Symptoms are Congestion and a Sore Throat.
Can be treated directly with Antihistamines.
Severity 1:
Level 1 Congestion, no sore throat.
Severity 2:
Level 2 Congestion, no Sore Throat.
Severity 3:
Level 3 Congestion, Level 1 Sore Throat.
Severity 4:
Level 4 Congestion, Level 2 Sore Throat.
  Stomach Flu:
An infection of the stomach lining, can be caught by eating uncooked or rotten food as well as drinking tainted water.
Symptoms are Nausea, Fever and Shivers.
Can be treated directly with Antibiotics.
Severity 1:
Level 1 Nausea, no Fever or Shivers.
Severity 2:
Level 2 Nausea, no Fever or Shivers.
Severity 3:
Level 3 Nausea, Fever and Shivers.
Severity 4:
Level 4 Nausea, Fever and Shivers. Risk of Death if untreated.
  Bleach Poisoning:
Bleach poisoning is a fast onset and fatal illness caused by directly drinking Bleach. It is always Severity 4.
Symptoms are Sore Throat, Pain, Anxiety, Shivers and gradual loss of Health.
Severity 4:
Level 4 Symptoms. Death is certain.
  Food Poisoning:
Food Poisoning is similar to Botulism but is caught by eating Poison Berries, Poison Mushrooms or food poisoned with Bleach.
Symptoms are Nausea, Sore Throat, Pain, Shivers and gradual loss of Health.
Severity 1:
Level 1 Nausea and Sore Throat, no others.
Severity 2:
Level 2 Nausea and Sore Throat, Level 1 Pain and Shivers. No loss of Health.
Severity 3:
Level 3 Nausea and Sore Throat, Level 2 Pain and Shivers. No loss of Health.
Severity 4:
Level 4 Nausea, Sore Throat, Pain, Shivers and a gradual Loss of Health. Can be fatal even with treatment if health already low.
  Rabies:
Caught by being Bitten by an infected animal. It is always Fatal if not treated with a Rabies Vaccine prior to Severity 2.
Symptoms are Anger, Stress, Weakness, Sore Throat, Agoraphobia, Pain when Drinking or Eating and Gradual Loss of Health.
Severity 1:
No symptoms.
Severity 2:
Level 2 Symptoms, but no loss of Health.
Severity 3:
Level 3 Symptoms, but no loss of Health.
Severity 4:
Level 4 symptoms and gradual loss of Health. Death is certain.
  Infection:
Caught by not properly treating a wound or spending a lot of time around corpses while your immune system is compromised.
Symptoms are Nausea, Pain, Shivers and Fever. If playing as a Hypochondriac, the symptoms are identical to Zombification if contracted from a Zombie Scratch instead but not always fatal.
Can be directly treated with Antibiotics or applying a sterilizing agent to the infected wound.
Severity 1:
Level 1 Nausea, no other symptoms.
Severity 2:
Level 2 Symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms. Can be fatal if left untreated.
  Scurvy:
Scurvy is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Vitamin intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Scurvy. Taking in the proper amount of Vitamins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Shivers, Pain and gradual loss of Health.
Can be directly treated with food rich in Vitamins or Vitamins medication.
Severity 1:
Level 1 Shivers and Pain, no loss of Health.
Severity 2:
Level 2 Shivers and Pain, no loss of Health.
Severity 3:
Level 3 Shivers and Pain, no loss of Health.
Severity 4:
Level 4 Shivers and Pain and the gradual loss of Health. Can be fatal if left untreated.
  Anemia:
Anemia is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Protein intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Anemia. Taking in the proper amount of Proteins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sleepiness, Weakness, Decreased Spatial Awareness, lowered item transfer rate and the gradual loss of Health.
Can be directly treated with food rich in Proteins.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Thyroditis:
Thyroditis is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Salt intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Thyroditis. Taking in the proper amount of Saltss will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sore Throat, Shivers and the gradual loss of Health.
Can be directly treated with food rich in Salts.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Zombification:
Caught by being Bitten or Scratched by a Zombie. It bypasses Immune system, with Bites always resulting in being infected and a 25% chance of being infected by a Scratch.
Symptoms are Stress, Sadness, Nausea, Untreatable Fever and the eventual death and rising as a Zombie.
Severity 1:
Level 1 Stress, no other Symptoms.
Severity 2:
Level 2 Stress, Level 1 Sadness, no other Symptoms.
Severity 3:
Level 3 Stress, Nausea, Sadness and Fever.
Severity 4:
Level 4 Stress, Nausea, Sadness and Fever. Death is certain.  
Abilities:
Players with high First-Aid or medical related Occupations/Traits will be able to deduce illnesses and administer medication directly to another Player, so Doctors and Nurses will have even more use in Multiplayer.
 
And that's that! Did I miss anything? What did y'all think?

Right now, the way disease is handled contrasts starkly with the overall complexity of the game...

My suggestion is to remove the ambiguity and turn certain Moodles into Symptoms, rather than have them as the disease themselves.
 
Symptoms:
Congestion:
Congestion replaces the Cold Moodle, becoming a symptom. It functions near identically, giving the player a chance to sneeze loudly, attracting zombies. Can be aided with an equipped tissue and treated with Antihistamines.
"Runny Nose"
"The sniffles"
"Congested"
"Severe Congestion" Fever:
Fever replaces the current Sick Moodle, becoming a symptom. Each stage will increase your character's temperature by a certain amount and will cause damage on its' highest level while also lowering healing, strength and increasing the rate at which a player gets sleepy. Can be treated with Antipyretics unless it is a symptom of Zombification. Equipping a Cold Pack that has been cooled in a freezer or a bag of Frozen Peas can also help.
"Bit of a Temperature"
"Temperature"
"Severe Temperature"
"Terminal Fever" Nausea:
Nausea is the other half of the current Sick Moodle becoming a symptom in its' own right. It lowers healing, strength and speed. It can be treated with Antiemetics.
"Bit Sick"
"Sick"
"Really Sick"
"Severe Nausea" Sore Throat:
A Sore Throat is similar to Congestion, but may cause pain when eating with an increasing chance to loudly cough which may attract nearby zombies. Can be treated with Cough Syrup.
"Scratchy Throat"
"Painful Throat"
"Rough Cough"
"Severe Coughing" Shivers:
Shivering which will lower the accuracy of the player. Can be relieved with Painkillers.
"A bit Shaky"
"Shaky"
"Shivering"
"Severe Shivering"  
While those are direct symptoms, other Moodles such as Pain would also be symptoms, directly or indirectly.

Medications:
Painkillers:
Relieves Pain and Shivers. Can cause Nausea if abused. Beta Blockers:
Relieves Panic. Antidepressants:
Relieves Sadness. Can cause Anger if abused. Sleeping Tablets:
Helps you sleep. Can cause Nausea or loss of Health if abused or taken while Drunk. Vitamins:
These should boost healing and help you recover some Immunity. Antibiotics:
Speeds up healing of Colds, Pneumonia, Infection and Stomach Flu. Can cause Nausea if abused. Caffeine Pills:
Relieves Sleepiness. Can cause Shivers if abused. Antihistamines:
Relieves Congestion. Can cause Sleepiness if abused. Antipyretics:
Relieves a traditional Fever. Can cause Nausea if abused. Antiemetics:
Relieves Nausea. Cough Syrup:
Relieves a Sore Throat, may also make you Drunk if taken in large quantities. Flu Vaccine Vial:
A vial containing a Vaccine for the Flu Virus. Can be added to a syringe so that you can administer a Flu Shot. Each Vial can fill a Syringe 4 times. Taking a Flu Shot will cause the Severity of Flu to begin to decline and will provide you with a month of immunity to the Flu Virus. Common Infection Vaccine Vial:
A vial containing a Vaccine for the Infection. Can be added to a syringe so that you can administer a Common Infection Shot. Each Vial can fill a Syringe 4 times. Taking a Common Infection Shot will cause the Severity of a Common Infection to decline and will provide you with a month of immunity to the Common Infection. Rabies Vaccine:
A vial containing a Vaccine for the Rabies Virus. Can be added to a syringe so that you can administer a Rabies Shot. Each Vial Can fill a Syringe 4 times. Taking a Common Infection Shot will cure Rabies, provided you take it prior to the manifestation of symptoms, and will provide you with a month of immunity to the Rabies Virus.  
There are a few others I'd like such as Morphine and so on that would have a chance to cause addiction, but the ones I've added are more to expand on what is present, rather than add too much new.
 
Items:
Pill Dispenser:
A container with random pills inside. Water bottle with Dissolved Painkiller:
As the name suggests. The Player can dissolve up to 4 units of Painkillers into a Water Bottle, allowing for Painkiller use to be stretched out, if a bit weakened. Surgical Mask:
Surgical Masks (along with gasmasks) provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, as long as they are at least 50% clean with no damage. Hazmat Gear:
A full set of Hazmat Gear will provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, so long as they are undamaged. Syringe:
A medical syringe used for injecting yourself with a Vaccine. Maybe also for Addictive Drugs. Empty Vial:
Garbage item left over when adding a Vaccine to a Syringe. Can hold water.  
Traits:
Strong Immune System:
Chance of catching a disease is halved. Can go well with Iron Gut and Outdoorsman for a Robust Genetics build. Weak Immune System:
Replaces Prone To Illness. Chance of catching a disease is doubled, more likely for a wound to be infected and faster Zombification. Iron Gut:
Chance of catching Stomach Flu from food or water is halved. Weak Stomach:
Chance of catching Stomach Flu doubled. Outdoorsman:
Being wet does not weaken your Immune System. Immune to Hayfever. Allergy Prone:
Very prone to Hayfever. Hayfever gained this way bypasses Immune System Variable with there always being a 10% chance of contracting Hayfever when moving through thick Vegetation in off seasons and a 25% chance in Spring. Resilient:
Less likely for wounds to become infected and slows Zombification. Asthmatic:
40% increase in running endurance loss, 30% increase in swing endurance lost and a chance to loudly cough when Exerted. Hypochondriac:
May develop infection symptoms without being infected. Easily Amused:
Slower rate of boredom and unhappiness. Depression:
Becomes bored faster and gradually becomes sadder with time.  
The Immune System:
The Immune System, or simply just the Immunity variable, determines the chance of becoming ill.
At 0%, you are fully healthy and won't get sick.
But any activity while Sick, Dirty, Bloody, Wet, Sleepy, Exerted, Sad, Injured or Hungry will cause it to gradually rise. At 1%, you have a 1% chance of catching a disease and so on.
Sleeping will help you recover your Immunity most of the time, however putting yourself to sleep with Sleeping Pills or Alcohol will prevent this recovery. Being well fed will also help you recover.
This variable is invisible to the player, as it is to a real person.
 
Severity:
When catching a disease, it will gradually rise in severity, before reaching a peak and lowering again in severity until the disease is gone. During this time, all you can do is treat symptoms and rest until you are better. There are 4 levels of Severity, based on when the disease's variable is at 1%-25%, 26%-50%, 51%-75% and 76%-100%.
Certain diseases, when treated with certain medications and the disease's variable reaches 0% will then be cured.
 
Nutrients:
There are many nutrients which a player will gain with a balanced diet. Lacking certain nutrients in your diet for too long will result in a Nutritional Disease. Nutritional Diseases bypass the immune system.
Calories:
Calories are the main weight determining nutrient. This value must be balanced with hunger consistently, or else obesity or anorexia may sneak up on the player.
Maximum: 3700
Minimum: -2200 Carbohydrates:
Carbohydrates are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Carbohydrates, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Lipids:
Lipids, previously called fats, are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Lipids, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Proteins:
Proteins are a determining factor in the increase and decrease of the Player's strength stat. Without the necessary proteins, the player will not be able to level up their strength. If a player consumes more than 400 Protein units, they will increase their strength in the same way as in the same manner as B40/B41. If the player consumes more than 700 Protein units, they will gain a 1.5 multiplier for strength increase. If a player's protein units falls below -250, they will start to lose strength, and reaching the minimum Protein units of -500 will result in the loss of strength with a multiplier of 2.
Maximum: 1000
Minimum: -500 Salts:
Salts can alter the rate at which a player becomes thirsty. This value is ignored unless the player has consumed more than 400 or 700 Salts resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Sugars:
Sugars are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Sugars, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Vitamins:
Vitamins are essential for keeping your Immune System strong. So long as the player consumes more than 400 Vitamins, their Immunity will recover as per normal while resting or sleeping. If the Sugar unit falls below 0, their Immunity will no longer recover.
Maximum: 500
Minimum: -500  
Diseases:
Diseases are visible in the Health tab when you have a certain level of First-Aid, but otherwise you'll have to guess by symptoms and circumstances.
Flu:
Sometimes, Zombies, Pigs (when added) or Chickens (when added) will spawn as infected with the Flu Virus. Being within 5 tiles from an infected zombie, the infected Zombie's corpse, an infected Player, an infected Player's corpse, an infected Pig or Chicken and an infected Pig or Chicken's corpse will make you vulnerable to catching the flu. Pigs and Chickens will also be at risk of catching it.
Symptoms are Congestion, Fever, Pain and a Sore Throat.
After catching Flu, there is a cooldown time before you can catch it again of around a month.
Severity 1:
The Flu is Asymptomatic at this severity, increasing the likelihood that you will spread it to other players unwittingly.
Severity 2:
Level 2 symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms, risk of death without treatment.
  Cold:
A cold is an ambient bacterial infection that can be caught when being wet, hot, cold or tired. Similar to Flu but far less severe but also far quicker to show symptoms.
Symptoms are Congestion, Fever and a Sore Throat.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Congestion and Sore Throat, no Fever.
Severity 2:
Level 2 Congestion and Sore Throat, no Fever.
Severity 3:
Level 3 Congestion and Sore Throat, Level 1 Fever.
Severity 4:
Level 4 Congestion and Sore Throat, Level 2 Fever.
  Pneumonia:
An ambient infection of the lungs that can be caught while Hypothermic. Similar to a Cold but far more severe.
Symptoms are Fever, Sore Throat and Shivers.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Sore Throat and Shivers, no Fever.
Severity  2:
Level 2 Sore Throat, Shivers and Fever.
Severity 3:
Level 3 Sore Throat, Shivers and Fever.
Severity 4
Level 4 Sore Throat, Shivers and Fever. Risk of death without treatment.
  Hayfever:
Can be caught by moving through dense vegetation during Spring.
Symptoms are Congestion and a Sore Throat.
Can be treated directly with Antihistamines.
Severity 1:
Level 1 Congestion, no sore throat.
Severity 2:
Level 2 Congestion, no Sore Throat.
Severity 3:
Level 3 Congestion, Level 1 Sore Throat.
Severity 4:
Level 4 Congestion, Level 2 Sore Throat.
  Stomach Flu:
An infection of the stomach lining, can be caught by eating uncooked or rotten food as well as drinking tainted water.
Symptoms are Nausea, Fever and Shivers.
Can be treated directly with Antibiotics.
Severity 1:
Level 1 Nausea, no Fever or Shivers.
Severity 2:
Level 2 Nausea, no Fever or Shivers.
Severity 3:
Level 3 Nausea, Fever and Shivers.
Severity 4:
Level 4 Nausea, Fever and Shivers. Risk of Death if untreated.
  Bleach Poisoning:
Bleach poisoning is a fast onset and fatal illness caused by directly drinking Bleach. It is always Severity 4.
Symptoms are Sore Throat, Pain, Anxiety, Shivers and gradual loss of Health.
Severity 4:
Level 4 Symptoms. Death is certain.
  Food Poisoning:
Food Poisoning is similar to Botulism but is caught by eating Poison Berries, Poison Mushrooms or food poisoned with Bleach.
Symptoms are Nausea, Sore Throat, Pain, Shivers and gradual loss of Health.
Severity 1:
Level 1 Nausea and Sore Throat, no others.
Severity 2:
Level 2 Nausea and Sore Throat, Level 1 Pain and Shivers. No loss of Health.
Severity 3:
Level 3 Nausea and Sore Throat, Level 2 Pain and Shivers. No loss of Health.
Severity 4:
Level 4 Nausea, Sore Throat, Pain, Shivers and a gradual Loss of Health. Can be fatal even with treatment if health already low.
  Rabies:
Caught by being Bitten by an infected animal. It is always Fatal if not treated with a Rabies Vaccine prior to Severity 2.
Symptoms are Anger, Stress, Weakness, Sore Throat, Agoraphobia, Pain when Drinking or Eating and Gradual Loss of Health.
Severity 1:
No symptoms.
Severity 2:
Level 2 Symptoms, but no loss of Health.
Severity 3:
Level 3 Symptoms, but no loss of Health.
Severity 4:
Level 4 symptoms and gradual loss of Health. Death is certain.
  Infection:
Caught by not properly treating a wound or spending a lot of time around corpses while your immune system is compromised.
Symptoms are Nausea, Pain, Shivers and Fever. If playing as a Hypochondriac, the symptoms are identical to Zombification if contracted from a Zombie Scratch instead but not always fatal.
Can be directly treated with Antibiotics or applying a sterilizing agent to the infected wound.
Severity 1:
Level 1 Nausea, no other symptoms.
Severity 2:
Level 2 Symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms. Can be fatal if left untreated.
  Scurvy:
Scurvy is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Vitamin intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Scurvy. Taking in the proper amount of Vitamins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Shivers, Pain and gradual loss of Health.
Can be directly treated with food rich in Vitamins or Vitamins medication.
Severity 1:
Level 1 Shivers and Pain, no loss of Health.
Severity 2:
Level 2 Shivers and Pain, no loss of Health.
Severity 3:
Level 3 Shivers and Pain, no loss of Health.
Severity 4:
Level 4 Shivers and Pain and the gradual loss of Health. Can be fatal if left untreated.
  Anemia:
Anemia is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Protein intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Anemia. Taking in the proper amount of Proteins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sleepiness, Weakness, Decreased Spatial Awareness, lowered item transfer rate and the gradual loss of Health.
Can be directly treated with food rich in Proteins.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Thyroditis:
Thyroditis is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Salt intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Thyroditis. Taking in the proper amount of Saltss will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sore Throat, Shivers and the gradual loss of Health.
Can be directly treated with food rich in Salts.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Zombification:
Caught by being Bitten or Scratched by a Zombie. It bypasses Immune system, with Bites always resulting in being infected and a 25% chance of being infected by a Scratch.
Symptoms are Stress, Sadness, Nausea, Untreatable Fever and the eventual death and rising as a Zombie.
Severity 1:
Level 1 Stress, no other Symptoms.
Severity 2:
Level 2 Stress, Level 1 Sadness, no other Symptoms.
Severity 3:
Level 3 Stress, Nausea, Sadness and Fever.
Severity 4:
Level 4 Stress, Nausea, Sadness and Fever. Death is certain.  
Abilities:
Players with high First-Aid or medical related Occupations/Traits will be able to deduce illnesses and administer medication directly to another Player, so Doctors and Nurses will have even more use in Multiplayer.
 
And that's that! Did I miss anything? What did y'all think?

Right now, the way disease is handled contrasts starkly with the overall complexity of the game...

My suggestion is to remove the ambiguity and turn certain Moodles into Symptoms, rather than have them as the disease themselves.
 
Symptoms:
Congestion:
Congestion replaces the Cold Moodle, becoming a symptom. It functions near identically, giving the player a chance to sneeze loudly, attracting zombies. Can be aided with an equipped tissue and treated with Antihistamines.
"Runny Nose"
"The sniffles"
"Congested"
"Severe Congestion" Fever:
Fever replaces the current Sick Moodle, becoming a symptom. Each stage will increase your character's temperature by a certain amount and will cause damage on its' highest level while also lowering healing, strength and increasing the rate at which a player gets sleepy. Can be treated with Antipyretics unless it is a symptom of Zombification. Equipping a Cold Pack that has been cooled in a freezer or a bag of Frozen Peas can also help.
"Bit of a Temperature"
"Temperature"
"Severe Temperature"
"Terminal Fever" Nausea:
Nausea is the other half of the current Sick Moodle becoming a symptom in its' own right. It lowers healing, strength and speed. It can be treated with Antiemetics.
"Bit Sick"
"Sick"
"Really Sick"
"Severe Nausea" Sore Throat:
A Sore Throat is similar to Congestion, but may cause pain when eating with an increasing chance to loudly cough which may attract nearby zombies. Can be treated with Cough Syrup.
"Scratchy Throat"
"Painful Throat"
"Rough Cough"
"Severe Coughing" Shivers:
Shivering which will lower the accuracy of the player. Can be relieved with Painkillers.
"A bit Shaky"
"Shaky"
"Shivering"
"Severe Shivering"  
While those are direct symptoms, other Moodles such as Pain would also be symptoms, directly or indirectly.

Medications:
Painkillers:
Relieves Pain and Shivers. Can cause Nausea if abused. Beta Blockers:
Relieves Panic. Antidepressants:
Relieves Sadness. Can cause Anger if abused. Sleeping Tablets:
Helps you sleep. Can cause Nausea or loss of Health if abused or taken while Drunk. Vitamins:
These should boost healing and help you recover some Immunity. Antibiotics:
Speeds up healing of Colds, Pneumonia, Infection and Stomach Flu. Can cause Nausea if abused. Caffeine Pills:
Relieves Sleepiness. Can cause Shivers if abused. Antihistamines:
Relieves Congestion. Can cause Sleepiness if abused. Antipyretics:
Relieves a traditional Fever. Can cause Nausea if abused. Antiemetics:
Relieves Nausea. Cough Syrup:
Relieves a Sore Throat, may also make you Drunk if taken in large quantities. Flu Vaccine Vial:
A vial containing a Vaccine for the Flu Virus. Can be added to a syringe so that you can administer a Flu Shot. Each Vial can fill a Syringe 4 times. Taking a Flu Shot will cause the Severity of Flu to begin to decline and will provide you with a month of immunity to the Flu Virus. Common Infection Vaccine Vial:
A vial containing a Vaccine for the Infection. Can be added to a syringe so that you can administer a Common Infection Shot. Each Vial can fill a Syringe 4 times. Taking a Common Infection Shot will cause the Severity of a Common Infection to decline and will provide you with a month of immunity to the Common Infection. Rabies Vaccine:
A vial containing a Vaccine for the Rabies Virus. Can be added to a syringe so that you can administer a Rabies Shot. Each Vial Can fill a Syringe 4 times. Taking a Common Infection Shot will cure Rabies, provided you take it prior to the manifestation of symptoms, and will provide you with a month of immunity to the Rabies Virus.  
There are a few others I'd like such as Morphine and so on that would have a chance to cause addiction, but the ones I've added are more to expand on what is present, rather than add too much new.
 
Items:
Pill Dispenser:
A container with random pills inside. Water bottle with Dissolved Painkiller:
As the name suggests. The Player can dissolve up to 4 units of Painkillers into a Water Bottle, allowing for Painkiller use to be stretched out, if a bit weakened. Surgical Mask:
Surgical Masks (along with gasmasks) provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, as long as they are at least 50% clean with no damage. Hazmat Gear:
A full set of Hazmat Gear will provide immunity to airborne diseases, such as the Flu and corpse proximity induced Infection, so long as they are undamaged. Syringe:
A medical syringe used for injecting yourself with a Vaccine. Maybe also for Addictive Drugs. Empty Vial:
Garbage item left over when adding a Vaccine to a Syringe. Can hold water.  
Traits:
Strong Immune System:
Chance of catching a disease is halved. Can go well with Iron Gut and Outdoorsman for a Robust Genetics build. Weak Immune System:
Replaces Prone To Illness. Chance of catching a disease is doubled, more likely for a wound to be infected and faster Zombification. Iron Gut:
Chance of catching Stomach Flu from food or water is halved. Weak Stomach:
Chance of catching Stomach Flu doubled. Outdoorsman:
Being wet does not weaken your Immune System. Immune to Hayfever. Allergy Prone:
Very prone to Hayfever. Hayfever gained this way bypasses Immune System Variable with there always being a 10% chance of contracting Hayfever when moving through thick Vegetation in off seasons and a 25% chance in Spring. Resilient:
Less likely for wounds to become infected and slows Zombification. Asthmatic:
40% increase in running endurance loss, 30% increase in swing endurance lost and a chance to loudly cough when Exerted. Hypochondriac:
May develop infection symptoms without being infected. Easily Amused:
Slower rate of boredom and unhappiness. Depression:
Becomes bored faster and gradually becomes sadder with time.  
The Immune System:
The Immune System, or simply just the Immunity variable, determines the chance of becoming ill.
At 0%, you are fully healthy and won't get sick.
But any activity while Sick, Dirty, Bloody, Wet, Sleepy, Exerted, Sad, Injured or Hungry will cause it to gradually rise. At 1%, you have a 1% chance of catching a disease and so on.
Sleeping will help you recover your Immunity most of the time, however putting yourself to sleep with Sleeping Pills or Alcohol will prevent this recovery. Being well fed will also help you recover.
This variable is invisible to the player, as it is to a real person.
 
Severity:
When catching a disease, it will gradually rise in severity, before reaching a peak and lowering again in severity until the disease is gone. During this time, all you can do is treat symptoms and rest until you are better. There are 4 levels of Severity, based on when the disease's variable is at 1%-25%, 26%-50%, 51%-75% and 76%-100%.
Certain diseases, when treated with certain medications and the disease's variable reaches 0% will then be cured.
 
Nutrients:
There are many nutrients which a player will gain with a balanced diet. Lacking certain nutrients in your diet for too long will result in a Nutritional Disease. Nutritional Diseases bypass the immune system.
Calories:
Calories are the main weight determining nutrient. This value must be balanced with hunger consistently, or else obesity or anorexia may sneak up on the player.
Maximum: 3700
Minimum: -2200 Carbohydrates:
Carbohydrates are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Carbohydrates, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Lipids:
Lipids, previously called fats, are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Lipids, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Proteins:
Proteins are a determining factor in the increase and decrease of the Player's strength stat. Without the necessary proteins, the player will not be able to level up their strength. If a player consumes more than 400 Protein units, they will increase their strength in the same way as in the same manner as B40/B41. If the player consumes more than 700 Protein units, they will gain a 1.5 multiplier for strength increase. If a player's protein units falls below -250, they will start to lose strength, and reaching the minimum Protein units of -500 will result in the loss of strength with a multiplier of 2.
Maximum: 1000
Minimum: -500 Salts:
Salts can alter the rate at which a player becomes thirsty. This value is ignored unless the player has consumed more than 400 or 700 Salts resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Sugars:
Sugars are used in determining potential weight gain. This value is ignored unless the player has consumed more than 400 or 700 Sugars, resulting in a multiplier of 2 or 3, respectively.
Maximum: 1000
Minimum: -500 Vitamins:
Vitamins are essential for keeping your Immune System strong. So long as the player consumes more than 400 Vitamins, their Immunity will recover as per normal while resting or sleeping. If the Sugar unit falls below 0, their Immunity will no longer recover.
Maximum: 500
Minimum: -500  
Diseases:
Diseases are visible in the Health tab when you have a certain level of First-Aid, but otherwise you'll have to guess by symptoms and circumstances.
Flu:
Sometimes, Zombies, Pigs (when added) or Chickens (when added) will spawn as infected with the Flu Virus. Being within 5 tiles from an infected zombie, the infected Zombie's corpse, an infected Player, an infected Player's corpse, an infected Pig or Chicken and an infected Pig or Chicken's corpse will make you vulnerable to catching the flu. Pigs and Chickens will also be at risk of catching it.
Symptoms are Congestion, Fever, Pain and a Sore Throat.
After catching Flu, there is a cooldown time before you can catch it again of around a month.
Severity 1:
The Flu is Asymptomatic at this severity, increasing the likelihood that you will spread it to other players unwittingly.
Severity 2:
Level 2 symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms, risk of death without treatment.
  Cold:
A cold is an ambient bacterial infection that can be caught when being wet, hot, cold or tired. Similar to Flu but far less severe but also far quicker to show symptoms.
Symptoms are Congestion, Fever and a Sore Throat.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Congestion and Sore Throat, no Fever.
Severity 2:
Level 2 Congestion and Sore Throat, no Fever.
Severity 3:
Level 3 Congestion and Sore Throat, Level 1 Fever.
Severity 4:
Level 4 Congestion and Sore Throat, Level 2 Fever.
  Pneumonia:
An ambient infection of the lungs that can be caught while Hypothermic. Similar to a Cold but far more severe.
Symptoms are Fever, Sore Throat and Shivers.
Can be directly treated with Antibiotics.
Severity 1:
Level 1 Sore Throat and Shivers, no Fever.
Severity  2:
Level 2 Sore Throat, Shivers and Fever.
Severity 3:
Level 3 Sore Throat, Shivers and Fever.
Severity 4
Level 4 Sore Throat, Shivers and Fever. Risk of death without treatment.
  Hayfever:
Can be caught by moving through dense vegetation during Spring.
Symptoms are Congestion and a Sore Throat.
Can be treated directly with Antihistamines.
Severity 1:
Level 1 Congestion, no sore throat.
Severity 2:
Level 2 Congestion, no Sore Throat.
Severity 3:
Level 3 Congestion, Level 1 Sore Throat.
Severity 4:
Level 4 Congestion, Level 2 Sore Throat.
  Stomach Flu:
An infection of the stomach lining, can be caught by eating uncooked or rotten food as well as drinking tainted water.
Symptoms are Nausea, Fever and Shivers.
Can be treated directly with Antibiotics.
Severity 1:
Level 1 Nausea, no Fever or Shivers.
Severity 2:
Level 2 Nausea, no Fever or Shivers.
Severity 3:
Level 3 Nausea, Fever and Shivers.
Severity 4:
Level 4 Nausea, Fever and Shivers. Risk of Death if untreated.
  Bleach Poisoning:
Bleach poisoning is a fast onset and fatal illness caused by directly drinking Bleach. It is always Severity 4.
Symptoms are Sore Throat, Pain, Anxiety, Shivers and gradual loss of Health.
Severity 4:
Level 4 Symptoms. Death is certain.
  Food Poisoning:
Food Poisoning is similar to Botulism but is caught by eating Poison Berries, Poison Mushrooms or food poisoned with Bleach.
Symptoms are Nausea, Sore Throat, Pain, Shivers and gradual loss of Health.
Severity 1:
Level 1 Nausea and Sore Throat, no others.
Severity 2:
Level 2 Nausea and Sore Throat, Level 1 Pain and Shivers. No loss of Health.
Severity 3:
Level 3 Nausea and Sore Throat, Level 2 Pain and Shivers. No loss of Health.
Severity 4:
Level 4 Nausea, Sore Throat, Pain, Shivers and a gradual Loss of Health. Can be fatal even with treatment if health already low.
  Rabies:
Caught by being Bitten by an infected animal. It is always Fatal if not treated with a Rabies Vaccine prior to Severity 2.
Symptoms are Anger, Stress, Weakness, Sore Throat, Agoraphobia, Pain when Drinking or Eating and Gradual Loss of Health.
Severity 1:
No symptoms.
Severity 2:
Level 2 Symptoms, but no loss of Health.
Severity 3:
Level 3 Symptoms, but no loss of Health.
Severity 4:
Level 4 symptoms and gradual loss of Health. Death is certain.
  Infection:
Caught by not properly treating a wound or spending a lot of time around corpses while your immune system is compromised.
Symptoms are Nausea, Pain, Shivers and Fever. If playing as a Hypochondriac, the symptoms are identical to Zombification if contracted from a Zombie Scratch instead but not always fatal.
Can be directly treated with Antibiotics or applying a sterilizing agent to the infected wound.
Severity 1:
Level 1 Nausea, no other symptoms.
Severity 2:
Level 2 Symptoms.
Severity 3:
Level 3 Symptoms.
Severity 4:
Level 4 Symptoms. Can be fatal if left untreated.
  Scurvy:
Scurvy is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Vitamin intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Scurvy. Taking in the proper amount of Vitamins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Shivers, Pain and gradual loss of Health.
Can be directly treated with food rich in Vitamins or Vitamins medication.
Severity 1:
Level 1 Shivers and Pain, no loss of Health.
Severity 2:
Level 2 Shivers and Pain, no loss of Health.
Severity 3:
Level 3 Shivers and Pain, no loss of Health.
Severity 4:
Level 4 Shivers and Pain and the gradual loss of Health. Can be fatal if left untreated.
  Anemia:
Anemia is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Protein intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Anemia. Taking in the proper amount of Proteins will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sleepiness, Weakness, Decreased Spatial Awareness, lowered item transfer rate and the gradual loss of Health.
Can be directly treated with food rich in Proteins.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Thyroditis:
Thyroditis is a Nutritional Disease that bypasses the Immune System. Each day a player goes without the necessary Salt intake from food or supplements will cause a variable to increase, once the variable is above 50%, the player will have caught Thyroditis. Taking in the proper amount of Saltss will lower the variable and if the variable falls below 50%, the Severity will begin to dissipate.
Symptoms are Sore Throat, Shivers and the gradual loss of Health.
Can be directly treated with food rich in Salts.
Severity 1:
Level 1 symptoms, no loss of Health.
Severity 2:
Level 2 symptoms, no loss of Health.
Severity 3:
Level 3 symptoms, no loss of Health.
Severity 4:
Level 4 symptoms and the gradual loss of Health. Can be fatal if left untreated.
  Zombification:
Caught by being Bitten or Scratched by a Zombie. It bypasses Immune system, with Bites always resulting in being infected and a 25% chance of being infected by a Scratch.
Symptoms are Stress, Sadness, Nausea, Untreatable Fever and the eventual death and rising as a Zombie.
Severity 1:
Level 1 Stress, no other Symptoms.
Severity 2:
Level 2 Stress, Level 1 Sadness, no other Symptoms.
Severity 3:
Level 3 Stress, Nausea, Sadness and Fever.
Severity 4:
Level 4 Stress, Nausea, Sadness and Fever. Death is certain.  
Abilities:
Players with high First-Aid or medical related Occupations/Traits will be able to deduce illnesses and administer medication directly to another Player, so Doctors and Nurses will have even more use in Multiplayer.
 
And that's that! Did I miss anything? What did y'all think?