I did not ever claim disability because I did not want questions like this, although I could have.
Not all forms of disability involve a broken back, or something like that, and not all are continuous (but most of the time). I have days where I could, fish, ride the motorcycle, etc., but not all that many.
I have degenerative disc disease. I can do alot...but not for very long and depending on what I do I may have to plan on spending the next day in bed.
Most people do not know that I have it because they see me at my best. Went to a huge BBQ today and I was ok. By the time we got home I could barely walk. If you asked the people there how I was I am sure they would all say fine.
I try not to let my condition stop me from doing anything I want but I know my limitations and I know there is absolutely no way I could hold down a job. Besides what employer would be ok with me working my tail off one day and calling in sick the next day.....every time.