You probably have a condition called Bruxism. This usually happens if you are under a lot of stress and think a lot. The immediate thing to do will be to get night guard trays made by your dentist. You have be under your dentist's constant observation for some time in order to evaluate the cause of the issue and a permanent remedy for it.

From what ur describing...it's not normal...u need night mouth guards...plz visit nearby dentist fr treatment

Had it been a normal thing you would not have been concerned enough to post it as a query. This habit is called as bruxism and has a subconscious root to it. There are physical as well as psychological factors leading to bruxism and these might not always be curable. But what we can do as an intervention is fabricate appliances called as night Guards which can be worn by the patient and they help to cushion about the forces of clenching so that the damage to the Jaws is minimised as much as possible. Absence of pain does not mean absence of disease and you should not wait for the symptoms to appear to seek treatment. Regards.