When I first started getting RSI, it was in the mouse arm, up near the shoulder. I did something similar, but wound up with a mouse on each side of my keyboard.

When I first started getting RSI, it was in the mouse arm, up near the shoulder. I did something similar, but wound up with a mouse on each side of my keyboard. That cleared it up reasonably well, and since then my main mouse has always been on the left. I think that the combination of a keyboard with a numeric keypad (wiiiide) and a right hand mouse is the main trigger, not the concentrated mouse usage with one hand. If I could find one of the narrow model M keyboards, I'd consider moving back to the other side. The other things I've done have all centered on being aware of where nerves are near the surface, and never putting pressure there. If you're getting numbness in the thumb and first finger, it's likely carpal tunnel. If it's all over, it's more likely at the elbow.