If there is some connection to "fitness" then you're on topic. Generally speaking though, wellness questions don't belong on the site. My question on ergonomics was deemed to be off-topic as another example.
Robert Cartaino's answer regarding injury/illness recovery is good criteria for determining what is on topic and what is not.
Dealing with exercise-related injuries are on topic.
"I pulled a muscle running. Apply heat or cold?"
Working around health-related issues in the context of reaching
physical fitness, on topic.
"I have allergies. What is a good exercise to replace my morning jog
when I can't go outside?"
- General medical/health "recovering from illness" questions (unless
there is a significant "physical fitness" component), off topic.
"What are the best remedies to speed up recovery from a cold?" — off
Medical questions shouldn't really belong on this site either, but it depends on the nature of it. Again, I would refer to Robert's answer. If you have to ask whether you should see a doctor or ask us (where there aren't any doctors at all), then you should go see a doctor. There's nothing stopping you from submitting to the "Health" proposal on Area 51.