I've read that tooth grinding is equivalent to your brain "twiddling its thumbs" :-) The suggestion was to eat an apple (something hard/crisp) or bagel (chewy) and sort of wear out those muscles and relax your brain's taking it out on your teeth.

I tried it (my dentist says I grind my teeth) and it seemed to help some. But I would definately go to your dentist and see what they suggest. I had a mouth guard made but they're kind of expensive and my teeth changed so it didn't fit anymore and I didn't find it comfortable for sleeping in, etc.