Nerves.I think it is fair to say we all get them in a performance situation. We are human, after all.
I thought it would be a good idea to discuss any methods you might use to help you
cope with them. I don't think you can eradicate them and it wouldn't necessarily be good to, anyway. What's important is finding a way to get on top of them.
Nerves can be a problem particularly affecting the performers breathing. If I allow myself to get too nervous then I start to breath in my upper body, which creates tension, which creates more panting...a perpetual cycle of pant-tense-pant-tense etc etc and this screws the voice.
Ironically the best thing I find to deal with nervous breathing is - breathing, but properly!
My tips pre-performance:
1. Warm-up and shake out. Be professional about this - give yourself time to loosen your limbs and shake them out and don't forget to exercise your voice.
2. Stretches. Hands above your head, onto tiptoes...s...trrrrr...etch! BREATHE in through your nose and out through your mouth. Work your diaphragm and NOT your chest. So breathe deep. Push your stomach out.
3. At the top of your stretch, flop forwards - time your breathing so you breathe out going down - like a mannequin has just had it's strings cut. Curve your back, hang loose. BREATHE as above.
4. Roll back up, through the base of the spine, breathing. Repeat steps 2-3 a few times.
5. When you get back to the top for the last time, just stand and breathe, as before. It's calming. Take the time to enjoy that space and that moment. Push right down into your feet and think of your breath reaching everywhere - into your toes, into your fingertips - every fibre of your being.
6. Now, still standing calmly, go over in your head what it is you need to do first for your performance. That will involve stepping out into the performance space - maybe even walking into position. It might be you have some lines to say, a song to sing, a dance to perform...visualise yourself taking those steps. BREATHE as you do it. Know in yourself what you intend to do.
Be calm.
Edit: Caffeine / Energy drinks. Mmm. I tried energy drinks before a performance once. Eeeek.

It'll be a banana next time, for me.