I recently stumbled upon some literature about neuroplasticity (the brain's ability to change structurally and functionally based on personal experience and use) and chronic pain. It sounds like there have been a few studies which suggest that the brain learns to be in pain - and once pain sets in it's almost like the brain overreacts. I found this really interesting video - http://neuroplastix.com/styled-2/page1/styled-7/raft.html
I'm thinking about looking into this for my own pain management!