Picked up a nail board and started clubbing some zombies only to find out they would never recover from being stunned. Some self-inflicted experimentation revealed that the same case was true for the player (I.E. Blindness would never go away.) I believe the game treats these as diseases, hence the title. I doubt the game’s intended to play this way, so here, have a bug report!
Edit: It seems “Glare” is a disease as well, causing players to have sunlight glares even in basements since the glare effect never goes away.