Honestly, it just sounds like a vagal nerve response, which is actually quite common and nothing to worry about:
http://www.healthguidance.org/entry/12051/1/Vagal-Nerve-Fainting.html
I wouldn't make an appointment unless it happens again, but definitely ask you dr and see what he/she says. :)
There could be a bunch of reasons. The best thing to do is call your doctor. You'll get thw right answer and it'll put your mind at ease a lot faster.