There's a really neat book called Gift of the Raven about an athlete with chronic knee pain that doctors couldn't figure out any plan to stop. He rowed from Alaska to Siberia and the book goes on about a shaman that performs a healing ritual (psychedelic mushrooms were involved) and he finds himself cured. So, there are times I suppose when the pain is all in your head, and maybe has a feedback loop since pain will also cause muscle contraction which can pull bones out of alignment. Relax enough and the pain stops.