Should You Practice Yoga When You are Sick?

One of my friends on Facebook asked me a very good question the other day: Should you exercise when you are sick?

I posted the question on my account to see if anyone else had any ideas & got some good responses:

"No cardio if its upper respiratory crud and no heavy lifting if you've got a fever, but, regardless of what you've got, a slow restorative yoga practice may feel relaxing, healing, and calming. :)"
-Joanne C.

"Doesn't it depend? A good sweat can help release what is in your body and especially help with congestion. Not a good idea if symptoms include fever or weakness. Also depends on exercise. Swimming, yoga, tai chai I think would all be ok if just a little under the weather. Curious to see what other and the experts say."
-Alicia M. A.

I know that in Bikram class if I have a runny or stuffed nose, I cannot breathe in certain postures, but I think that if i was REALLY sick, not only would I want to stay home to rest, but I wouldn't want to pass on my germs to others in class.

What are your thoughts about practicing Yoga when you are sick?