I wish I knew! I get that way in crowds a lot, but sometimes even in safe, familiar environments only a few extra people. Even in high school with my friends, I sometimes got jumpy and just had to go hang out by myself for a while. Now I recognize it as anxiety but I sure as heck don't know why it's intermittant. It doesn't seem to make any sense. Share any answers you may find. It may be helpful to some of the rest of us.