I'm a guitarist, but happened to see this on the main page. And since I'm suffering from the same problem, just thought I'd drop by and share my experience.
I used to sling my guitar real low for a few years. This caused a strain to my wrist and forearm after some time, especially during 2-hour jammings. At first I ignored it, 'cos with the guitar slung low, it looks cooler I guess, and pain was secondary at that time. But with the pain not going away after quite some time, I had to raise the guitar to a height where I can play comfortably and not strain my hand.
Problem is, it may already have been too late. I believe the damage I've caused is already permanent. These days, the pain comes-and-goes. It is really annoying, especially at work, 'cos I work a desk-bound job and have to use the computer. The pain can get so bad at times that I can totally drop something I'm holding out of my hand because the pain just comes at me like static.
Have a feeling it may possibly be a diagnosis of Carpal Tunnel Syndrome, 'cos the symptoms seem to point in one direction, but am not opting for an operation as I seem to be handling it well. These days, I get by with painkillers prescribed by my company's doctor. Just pop one in if need be.
You could possibly try painkillers if you feel the pain while playing, but remember, these aren't long-term solutions. If the pain persists (especially when you're not playing), see an orthopaedic specialist. I consider myself very lucky to have not gone to the extent of having to undergo surgery. Please do look into your problem before the damage becomes permanent.