Grinding teeth when sleeping. what does it mean?

Damaging: can be from illfitting teeth, stress, a host of things, BUT it damages teeth and a bite guard works well

See a dentist : Parafunctional habit like bruxism or grinding can be caused by uncoordinated masticatory muscles or ear problems. A dentist may recommend a mouthguard but if you already have ringing of the ears and headache, you need further assessment by a dentist who has a background in TMJ, orthopedic, and orthodontic. When the TMJ and bite is already balanced, that is the best time to have a cosmetic work.

Not good: Bases on your associated symptoms of head pain, tinnitus, and ear pain, it means your are causing damage to the jaw, and maybe to the teeth. Talk to your DDS about a nightguard.