I kind of understand what you mean, but to a much lesser degree. Whenever I perform on stage (very often, but nothin changes!) I always need looooaaads before hand. I keep on goin and goin, and get paranoid that I still need. The same happens before big events, like exams and what not. Could well be the case that there is a link.
Whenever I do get on stage though, or sit an exam, it stops pretty much instantly. Ive gotten to know this over time. The pre-event nerves are absolutely nothing to go by. Yes they can be bad, but as soon as you do something they disappear, its all good.
Hopefully it'll be exactly the same for you. Try to not let it stop you doing things.