Seeing a dentist is advised.
Have you had dental procedures done recently, like maybe a root canal? If you end up needing a root canal please go to an endodontist and not let a general dentist do it.
You could have the start of periodontal disease and just need a very thorough deep cleaning, or it could be from night grinding and clenching your teeth.
Whatever the reason, you really should be evaluated by your dentist to be sure.
Best to you,
Gellia