Pain disorder is when a patient experiences chronic and constant pain in one or more areas, and is thought to be caused by psychological stress. The pain is often so severe that it disables the patient from proper functioning. It can last as short as a few days, to as long as many years.
The disorder may begin at any age, and more women than men seem to experience it (APA, 2000). This disorder often occurs after an accident or during an illness that has caused genuine pain, which then takes a life of its own.

Info Source, Links and more info:
http://en.wikipedia.org/wiki/Pain_disorder