Whenever I come out I always feel sick to the stomach. Even when I came out as "not straight" to the GSA.
Saying "I'm Gay" or "I'm not Straight" is one of the hardest things you can say to someone. I've done it dozens of times and I still get a bit nervous during the build up and (depending on the reactions) the aftermath. The sick feeling is likely to just be a release of pent up nervous energy. It's completely normal.
what mangotree said...plus, you know, you are still pretty hung up on the idea that you want to be straight still so you're going to feel bad admitting it for a while...