i twitch whether i'm nervous or not. my head will do a little "bop" here and there through out the day, my nose twitches, my eyes, and then i shake my foot a lot whenever i'm sitting down. i never notice until someone tells me, then i get rather embarrassed about the whole situation
i try to make myself stop, but that only lasts for so long. it's pretty much ingrained in me to do these things without command.