Currently, character can become panicked only if he sees zombies, so I decided to write a short list of things that can make you panic.
1. Witness murder at first times.
2. Being surrendered by zombies outside the building.
3. Triggering home/vehicle alarm.
4. Being inside burning building.
5. Falling from roof.
6. Sudden zombie appearance (from behind the corners and trees e.t.c).
7. Being under fire.
8. Being damaged.
9. Got bitten.
10. Idk what to add. You can continue list in comments.