Fatigue and anxiety can become a cycle. I get this sometimes but not to the extent you described (being bed bound for three months). When I exercise for the sake of exercise it doesn't seem to help because I'm too conscious of the fact that I'm trying to get over the anxiety and fatigue, so I get more anxious and more fatigued. The trick is to try to find something you really enjoy that also gives you some exercise- hopefully something that takes your mind off of it entirely. I take walks with my camera and photograph nature. When I'm looking for birds or setting up a photograph I don't think about anything else, and this is the best way for me to get out and be active. Also, be sure to ramp up gradually. Don't dive right in or you will make yourself worse. And... it takes time. Be patient with your body. You might even start to feel worse before you start to feel better.