I think there are several things you can do here.
First off- you're not alone. Believe me, plenty of performers suffer from anxiety of some kind or another. That's a good place to start. Just knowing you are not alone will help. A lot of people self-medicate which is something I don't adhere to. I want to be on top of my game, so no drugs, no alcohol. I get dingy enough digging the vibe.
Anxiety is a physiological state brought on by psychological state. IOW- it's triggered by something ingrained in your thought. I've studied psychology for years and I've learned a few things about this. A few tips-
1. Don't think about the performance. That's what rehearsal is all about. Iron out problems in rehearsal so they don't pop up during performance. If they do pop up in performance, improvise and make a mental note to address the problem @ the next rehearsal.
2. Don't expect perfection. Do the best you can but realize that we are all human. We all make mistakes. We all fail from time to time but we work through it. Yes, you strive to do your best but don't let a mistake blow your mind. It happens to everyone.
3. Get to the gig early and chill. Work on things that could become problems to take your mind off the gig. This is a good time to meditate.
Just remember that the physical symptoms are a by-product of a mental state. Get the mental state in tune and the body will follow. If it's a BIG problem, talk to a doctor.