You've lost 140 pounds and don't have a sense of self worth? Are you sure your not looking in the wrong place for it? I think the sense of self worth is a big part of you doing something that most people only wish they had the strength of will and grit to accomplish.

In my spinning class last Thursday a young man came in with his wife, after dinking around for about 15 minutes of the class (rolling his eyes at the instructions) and taking up a bike that we could have used for a serious cyclist he finally just got up and left without even a shred of courtesy to the instructor or class. There is a guy who (even though he lacks the wit to know it) had an embarassing cycling class. You just had a bit of a fall and haven't a thing to be embarressed about.