I've not had this problem related to using a mouse, but severals ago I was involved with a major project that involved an enormous amount of copying/cutting and pasting using Ctrl+C; Ctrl+X; and Ctrl+V. This went on for 8 hours per day over about 6 weeks. I had developed a rhythm which allowed me to put my brain in neutral. (OK, I know that's the state many believe I live in all the time

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Everything was OK until the final week when I began to experience severe pain in both wrists. The problem seemed to be related to the stretching between thumb and little finger in my small hands.
I took some anti-inflamatory tablets, used a cream (available in Australia as Dencorub) and wore elastic supports (available from pharmacies) that covered the base of my fingers, all of my thumb, extending to include my wrist.
I was lucky, because after several weeks of applying this treatment and stopping the repetitive actions, everything returned to normal.
Re Paul's comments: I find that when I switch to using the Notebook with the supplied smaller mouse, I can feel a twinge returning to the joints in my right hand. Like Paul, I find this is exacerbated by using a small, light-weight, corded mouse.