See a medical professional! That said, anecdotal not-medical-advice: I had mousing-related pain, and I fixed it by mousing left handed. The first couple of day

See a medical professional! That said, anecdotal not-medical-advice: I had mousing-related pain, and I fixed it by mousing left handed. The first couple of days were incredibly frustrating, but after a week I had probably 80% of my right handed dexterity. To prevent the same issue from building up in my left hand, I started alternating between left handed and right handed mousing every couple of weeks. I guess the worst case outcome here is severe damage to both hands, so proceed with caution.