I have a very sick sim named Duto. Sick, not weakened. I noticed when he first got sick, (not event related) and his bar was barely showed any white. He happened to be my only healer, so I took somebody, Ema, with not even a single pixel of healing ability to heal him. Ema is now an adept doctor just from trying to heal Duto. Duto's health meter is down about a fifth now and he's still sick.
I have plenty of food and Medicine is at level 2, but I'm nowhere near getting level three. Only 24000 points and too many other things to buy first. I tried leaving the game and coming back and he's still sick. He's only 40 years old.
This is my second time through the game and this never happened to me before. I can't stand hearing his little coughs. It breaks my heart.