canuck,
first of all, Happy B-Day! i can understand how you feel. i'm so nervous and jumpy that i flinch when someone around me makes too sudden of a movement b/c it's still my instinct; i think they are going to hit me.
Anyway, don't feel ungrateful; you told them how you felt and they didn't listen. I'm sure you're grateful, and i don't think that you should feel bad about not feeling up to a party. you DID convey your wishes to your bf!! That's just my opinion. i know how hard it is to put on a "happy face" and fake your way through certain events. i, too, have had similiar circumstances where i had to act "happy" or "normal"...
Hang in there!