Ouch, i have done that before too.
My buddy just had hand surgery this week from the repetitive stress of sanding during stratchbuilding and kit building, they had to do something with the nerve sheath or something like that. They may need to do his shoulder too, same issue repetitive stress.
Guess it means that just because you can so something for hours on end, does not mean you should.
Take care of those hands.
Not until late next week, the next few days will be keeping me otherwise occupied. I have taken most of the past week to further refine and wet-sand the existing parts which were rough. A little too much hand-sanding on my part, my thumb started to bleed from the constant pressure and abrasion from the sandpaper so it will be much-needed recuperation time.