With my illness it's really hard to even get out of bed. What all my doctors tell me is that I have to try to do physical therapy even if it's only for 5 minutes a day. I know what you're thinking-5 minutes is kind of pathetic. But for me, 5 minutes of exercise is like a normal person running 5 miles.
Let's say you are healthy though and are running the 5 miles. Whether you finish in 30 minutes or 3 hours doesn't matter. What matters is that you're not giving up.
I know this is super over used and cliche but think if the tortoise and the hare. The super slow tortoise won! Because guess what...HE DIDN'T STOP!!!!!