I was depping on the organ the other day in a normal parish church near here. It was communion, and the choir was trying to sing And Didst Thou Travel Light by Richard Shephard under my direction from the piano.
Just before they started, I noticed a Very Important Organist sitting in the congregation. Why he was even there, I don't know - I'm sure he could have had better places to be (he used to play at Westminster Abbey!).
I was fine earlier in the service, but after I spotted him, I simply could not play the right notes for all the chatter going on in my head. I kept saying to myself to concentrate on the technique, to try not thinking about him thinking about me. I wished I had practised the voluntary more, and not tried to wing it.
This, I think, must be what kids think in exams. I understand, now.
There are many techniques to help overcome Performance Anxiety - check out the link below.