Sounds like you need to quaff a pint before you play!!
Ha! Think that'd help? Seriously, I used to play at an open mike in a nearby town (restaurant had the sound equipment, musicians could just show up and play for five or ten minutes at a time). My first few "performances" were sooooo bad because I'd get terrified, my arms and hands would completely lock up, and I would literally be unable to play. I didn't just flub a few notes - I actually had to stop, apologize for the attempt, and leave the front because my hands were so locked up I couldn't so much as strum. After I did this a couple of times in a row (I'm a glutton for punishment, I guess...or wanted to prove I could do it), SEVERAL people offered to buy me a drink for before I tried again...
I'm much better now than I used to be...now I just think too much! I still have a tendency to play better when I'm kinda sleepy and not so worried about what I'm doing, though.