Why do my hands cramp when I become overheated?

I've been in a Sweat Lodge about 15 times, and twice, my hands cramped shut. I've recently started Bikram Yoga, and I've experienced the same symptoms. There is no pain at all, and it doesn't feel bad anywhere else, and it doesn't scare me. The cramps go away anywhere between 10-20 minutes. I can't pinpoint what causes this - I am very hydrated, drinking water and Gatorade-types of drinks as well. So, I just want to make sure I'm not overlooking something that could be dangerous.