Have you ever looked into the Hofi Hammer method? It completely changed the way I forge and greatly reduced hand fatigue/shock. I no longer lean over the anvil, can forge for longer periods of time, was able to increase my max hammer weight by 2lbs and my hand/arm/shoulder/back feels better than ever. When using the method, you are mostly gripping with the thumb, index and middle finger, with your palm facing the anvil, as opposed to the knuckles down traditional hammer grip. The technique is a whipping motion and the hammer head travels in a straight line, up and down. Imagine yourself bouncing a basketball. The key to the whole thing is that you are only assisting the hammer rather than driving it. You apply force to the hammer only during the stroke. Upon impact, you essentially release your grip and catch it on the rebound. Buy the DVD, you won't be sorry.
But I agree, when you are hurting, it is best to take some time off. Quick healing!