You asked: "Wouldn't it be nice to KNOW how this disease / disorder starts? Maybe, then we could treat it more effectively."

I agree. I think the likely cause is fluoride poisoning. But not everyone who ingests significant amounts of fluoride gets fibromyalgia. Here are some further conjectures on my part.

Assume that fibromyalgia is caused by fluoride poisoning.

Then fluoride poisoning will bind to and therefore lower available magnesium and calcium. Fluoride may also facilitate the transport of aluminum to the brain.

Many people in the US, but not all are magnesium deficient. It seems to me that if a person is already deficient in magnesium then they will manifest symptoms of fluoride poisoning sooner than someone who is not magnesium deficient. For many processes in the body, even if a person is not calcium deficient, if they are magnesium deficient, the available calcium cannot be used without sufficient magnesium.

People who suffer from fluoride poisoning may manifest different severities of certain symptoms depending on how much aluminum they take in. The more people use baking powder, drink from aluminum cans, use aluminum foil (have you ever seen pin holes in foil you have taken off of some stored foods? Guess what, that food now has some dissolved aluminum in it), use alum or other aluminum containing deoderants, use aluminum cookware - the more aluminum could be transported to their brains by some mechanism involving the fluoride in their bodies.