I was hit by an firefighter axe. The screen lost a bit of color.
I bandaged myself and after that I applied alcohol and antibiotics. The "sick" status appeared.
I logged out and played again on the next day:
My character was healthy and full fed before. So the regen started immediately.
The colors were fully back after about 20-30 minutes.
My inventory still shows that I would be sick, even after 6-7 ingame hours ( full-fed and full-drunk for the whole time)