What causes hands to clench up during sleep?

I do this also: There may be several factors. It could be a response to the stresses in our lives. Some people clench and grind their jaws and teeth and some people exhibit their tensions elsewhere. Clenching my hands has exacerbated my carpal tunnel condition causing tingling in my hands. I now where a brace to help prevent me from clenching my hands. You may want to see a hand specialist, i did.