Muscle cramps - I get them, I've always gotten them, since I was a teenager. Make sure you're getting all your minerals - it can be diet related. Other than that, heat will relax the muscle. Heating pad, hot water bottle, or if you can, stick whatever is cramping into warm water, like in the tub or sink.
Sometimes I get them in my feet when I'm driving - I used to drive a straight shift, and would have to pull over, get out and walk it off. Ouch!