Well, thanks to everyone who contributed thoughts and advice.

I played a gig tonight and actually managed to enjoy it. I was less nervous to begin with because half the audience who would normally have been there were at home watching the footy, but I did put some of the advice into action, namely:

1) I had a SMALL drink (enough not to affect my driving by going home time)
2) I talked to the audience and smiled between numbers
3) A number seemed to start out of tune so I stopped it and made us retune (actually it wasn't any better so perhaps it was just my imagination)
4) I forgave myself for the imperfections and lived with the PA not being quite as I would have liked.

And lo and behold it worked. I enjoyed it, the audience thought it was great, and a good time was had by all.