The music I play it is very demanding, and my expectation is high, even though the audiences don't care less whether or not I can achieve it or not.
I wonder if this is part of it. I play for church services, despite being relatively unskilled compared to the rest of you. But there was nobody else available. Sometimes I can relax and just play. Other times I dread the next piece, and sit waiting while my anxiety builds wishing I'd overslept or called in sick. <grin> That really takes the fun out of it! The problem for me is that given my skill level and the time I have to prepare, I am often playing way over my head, with a train wreck just one note away. In my case that's where the fear comes from. When I play something simple and familiar, I can relax and enjoy it. Could you scale back the difficulty and still please the audience? What I'm suggesting, I guess, is that your anxiety may be justified due to the level you are attempting. And that your anxiety may well diminish greatly if you're playing repertoire you know you can do well.
I went to a recital by Renée Fleming where she actually had a microphone just so she could talk between numbers.......Actually a lot of singers do this, but I don't recall a pianist doing it. They just rush out from the wings and plunge into the music. But don't y'all think Glenn Gould and Vladimir Horowitz would have had less stage fright if they'd chatted with the audience? Gould could be quite chatty in other situations apparently.
There are a lot of phobias out there, and public performance/speaking is one common amongst many people. The "fear" of public performance is often a very deep psychological issue which must be dealt with in a careful manner.I find in my own students the fear for performance has nothing to do with music itself. It has more to do with a confidence issue with past experiences in public performance. Anyone who has anxiety as soon as multiple eyes watch them has to realise that this fear was learned, and acquired in the past when we where younger. A lot of this fear comes from public school where you had to perhaps read out loud to a classroom and was embarrassed you couldn't read the words as well as other people. It would be when a teacher told you to stand up infront of the class etc etc. We must learn to pinpoint where our fear where learnt from, then we can really get our hands around it and control and change our fear.