Persistent pain after stressful events may have a neurobiological basis

"Our study findings indicate that mechanisms influencing chronic pain development may be related to the stress response, rather than any specific injury caused by the traumatic event," said Samuel McLean, MD, MPH, senior author of the study and assistant professor of anesthesiology. "In other words, our results suggest that in some individuals something goes wrong with the body's 'fight or flight' response or the body's recovery from this response, and persistent pain results."
http://medicalxpress.com/news/2013-05-persistent-pain-stressful-events-neurobiological.html