Bruxism occurs when you grind your teeth and clench your jaw during sleep. It can become a habit or it can be due to stress or certain medications. If you find that you wake up with an aching jaw and/or neck, then this could be the cause of this discomfort. It can also cause headaches due to tension that is created. There are simple treatments available from a dentist, and these should be sought as untreated Bruxism can cause damage to your teeth. Your dentist can make a guard for your teeth from an impression of them and this can be worn at night to reduce the grinding.