Any human behavior pattern including Ischemia (reduction of oxygen in the extremities) can be conditioned or programmed. Sitting, walking, squatting, picking up a pencil can all function as physical triggers for mind-body symptoms. I believe Dr Sarno gives an example of this in the first few pages of Healing Back Pain where he speculates that at the time of the onset of pain symptoms someone sits at a computer and begins to associate sitting with the pain. A behavioral psychologist would call this a conditioned response. To cite a more prosaic example, why do you blush when you get embarrassed or get goose bumps when you watch a scary movie? Same phenomenon. Of course, it's absolutely essential to get checked out by an M.D. to make sure there's no physical cause for the pain. But sitting in a chair triggering the onset of TMS symptoms is very, very common.
Anyone else want to weigh in on this phenomenon?