This is an excerpt from a post I just made on an acoustic guitar forum in a similar thread. You already seem aware of R.S.I. and its horrible implications, but for anyone who isn't, please read on (even if it is a bit of a lecture). This is a condition that really has to be taken seriously.

The trouble with R.S.I. is that (a) it often doesn't hurt enough to really stop activity, so people stoically carry on and try to "work through" it: a disastrously wrong approach for R.S.I.; (b) it can escalate in stages, so that people go for a period of time with a nagging but bearable amount of pain until one day it's so much worse that they can't use their hand/shoulder properly at all; (c) this is a worst-case scenario, but if this sort of wear-injury is persistently ignored it can permanently cripple the affected area. I'm not exaggerating or trying to scare-monger. It can and it DOES. The websites and blogs are full of people saying "if only someone had told me".

Computers are the worst culprits because they use repeated tiny movements rather than the larger actions required by the old manual typewriters. It can also be caused by knitting, playing an instrument, or anything that makes you do the same movement over and over.

The other thing to be aware of is how you're sitting, especially if you're using any muscle tension in your back or shoulders to "hold" yourself in place. This can have a huge effect on how much stress is being put on the tendons. You can be tensing something in the shoulders or neck that will manifest down at the wrists, for example.

There are some very helpful R.S.I. chat/help forums. You really have to stop playing altogether until it heals, which could be a matter or weeks or months depending upon how bad it is. But it's better than stopping permanently, which is a very real alternative. The only way to treat wear is to stop doing whatever causes it and let the body rebuild itself.