Believe it or not, when I was a student in my emergency medicine rotation we actually had a young man come in to the ER with the complaint of being calm. Because he was anxious every single day. And he felt there had to be something wrong with his body if he wasn't anxious......the good news being that we didn't find anything wrong, but it was a challenge trying to find a way to help him.
I don't quite get this sensation myself, however I've found that I can't meditate at the end of my lunch hour especially if I have a 1:00 PM patient. I can't tolerate the abrupt shift from full stillness and calm to jumping back into the routine, I get some rebound anxiety from that.