I just ready a report that over 3 million people in the U.S. suffer from bruxism. In layman's terms, that means grinding your teeth, usually while you sleep. This is usually caused by stress, nervousness, insomnia or other psychological issues, but the result is rough on the teeth.
First, you end up grinding the enamel off your teeth. You can also be causing minor fractures in your teeth, weakening them and allowing bacteria to pass all the way to the root of your tooth. But losing the enamel is bad enough. Enamel is hard, what's below it isn't, and it decays a lot faster.
People also get headaches that are the result of bruxing or grinding. You can imagine that clenching your teeth against each other for hours would make your jaw tired and pretty quickly make your head ache.
Some people try to compensate for the damage done by bruxing by getting cosmetic veneers on their teeth. Unfortunately, many times these will break or pop off because of the continued pressure from the bruxing.
The only solution is seeing a dentist and treating the bruxism with a well-fitted night guard that both protects the teeth and puts the jaw in the right position. Don't try to find some cheap thing that you get in a drug store. This mouth guard, or dental splint, should fit perfectly, and only a dentist can make those measurements and design something that works.
And then try to relax. Think about meditation, vacation, or at least taking a few deep breaths every day.