Ugh; I'm sorry you're feeling cruddy. I had a bad case of the flu in 1999 (that I remember all too well to this day). I became delirious on about the 4th day of it because my fever climbed above 105 degrees. It was bad. Thankfully, I had a roommate at the time who had enough sense to contact my doctor, who got me sorted out. Anyway, I remember feeling rather weak for a good month after I recovered.
If I were you, I'd make sure I was getting a steady dose of iron, the B vitamins, vitamin D, potassium, magnesium, calcium and zinc. I would take it incredibly easy on the exercise front for at least another two weeks. Right now, it sounds like you don't have much choice, but when you do start to get some energy and strength back, be careful not to over do it. I'd stick to recovery pace workouts (heartrate no higher than 65% of max) and cut them short. I'd probably stick to low impact exercise, too.
Feel better soon!
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher