A not-so Offhand Hypothesis

I have noticed this for a couple years-   I have now seen enough examples to state it publicly.

Fibromyalgia is not an independent illness:  it is an adverse effect of chronic dental infection.
The toxins invade the nerves in the jaw and filter down into the neck and shoulders.
Eventually the nerves in the mouth die and stop hurting, but the ones down below still cause pain.

My own experience convinces me-
Shoulder twitching and pain is a sign your teeth need fixing.