I know it was never actually in the game, but back in the Desura days I am fairly certain there was a time that it was mentioned about being a possibility, I also remember the emote icon for maximum tiredness when moused over would say "in danger of passing out" or something like that. Obviously, that wouldn't make sense if being chased by zombies lol, but yeah. The vision difference has honestly never been enough in my opinion, at least if somebody stays up for days and days these other effects would be good to come into play.