@sozobe,
I'm not sure what it is, but it's definitely something.
It's like the folks with Crohn's, which has a huge psychological impact/component. Hard to understand the connection, but it's clearly visible if you've had a number of clients with the Crohn's dx.
I'd like them to pursue the research much more, as it is clear that many observers think it's "all in their heads". Well, knee bone's connected to the ... etc etc. Mind/body connection and all that.
They could well end up physically and emotionally buggered up, but it does seem to be some disease process that starts it off.