You could be grinding your teeth at night which is making your jaw muscle inflamed. It's not necessarily from Fibro, but stress, which Fibro causes. You could try a mouth guard.

It may be TMJ =Temporal Mandible Joint pain

I have jaw pain on the right side and I did go to the dentist and he prescribed a mouth guard. It has really helped.

Sometimes but way worse when wearing denturez

I was just looking up why biting cheek in my sleep, looking to see if the inside cheek is swollen. And there are days have discomfort in jaw area and chewing.