I dont like using mouse much.. Ive found too that my hand parts start spasming if Im using a mouse too much. Instead I use the touch pad.. often at in a diaganal kind of way with my hand resting on on the computer and will use any finger to press the other parts.
brain cramp
.. I think I know what you mean. I get that too if Im having to focus too hard on something.. it makes my head quite uncomfortable (its not a headache as such but something else.. it can actuallly hurt thou with the pressure of it)... I end up having to stop and rest my brain.