I know people who have panic attacks and true social anxiety. I'm fortunate enough that I don't. I have just enough anxiety to make me worry about absolutely every detail, and enough self-awareness that I feel (and act) incredible awkward in new places or with new people. A previous employer told me that my interview was one of the worst he had ever seen. He hired me anyway, based on my references, and it was a year before he told me how awful I had been — after he realized that I wasn't a complete fruitcake.
What bothers me the most these days is that I miss out on events that I think I would really enjoy because I completely psyche myself out of going. Or, if I do go, I have second, third, and fourth thoughts about it and present myself like babbling idiot. Or stand-offish. And I know I am doing it and am helpless to stop it.
So, bear with me if you invite me to something and I don't show up, or maybe worse, I do show up and immediately lurk in a corner making awkward eye contact with people walking by.