I know it sounds kinda cheesy but when you are feeling sorry for yourself, take a look around and I'm sure you'll see someone in worse straits. The reflect on the good you do have, and find an way to help someone less fortunate.
I was in acute rehab hospital and there were so many people with worse problems (like not being able to swallow) I really couldn't ever get down on why I was not functioning as before!
Even though I couldn't do much on my own, I did meet someone who was super nice, and was embarassed because she was crying all the time. No one took the time to spend with her and just be a friend. It helped both of us to sit and talk, and really made me reflect on my situation.