I know a guy who gets so nervous in front of groups that the entire left side of his face freezes -- like he's had a stroke or something. It's awful for him. I think you should get it checked out to rule out neurological causes. Good luck (and Rapunzel is right -- you're probably way more aware of it than the people you are talking to).

Also, I do get major eye and leg twitches when I'm under stress. My doctor did a blood test for electrolyte levels and said that insufficient potassium intake can cause muscle twitches. Maybe that's something you could have looked at as well.