I have the same problem as you, right before I perform a play. Try not to eat too much, I have made that mistake, and keep telling yourself you can do it. It's okay to be nervous, and almost everyone does. Don't worry about what your about to do, and just keep telling yourself that even if something unplanned happens you still tried your best.
Well I'm a dancer so I always get nervous performing in front of all those people because there is so much to mess up on in dance. Right before I go on I take a deep breath and that seems to help. Smile and remember to have fun. After you do whatever your doing it will be easy and fun and you might wanna go do it again. When I dance I'm nervous so I take a deep breath I go out dance my hardest smile and have fun and when I'm done I just wanna go out there and do it again. Hope this helped It might have been a little confusing Good luck:D -Beth<3
You did not say if this is before an event or that you are nervous in general. If it is just in general you need to go to the doctor and make sure you do not have a physical problem. Start the day out before the Lord by reading His Word (the Bible) and prayer. Ask for calmness. He may not give it that minute because He wants you to relay on Him always, but In time you will realize that you or feeling better.
Try not to drink any beverages w caffiene. U could be sensitive to stimulation. High anxiety becomes a learned response. If it becomes unbearable go see a psychiatrist. Medication can help so don't be afraid to take it. It's better than suffering.. Good luck. ;)