What causes fibromyalgia or chronic fatigue syndrome?

Fibromyalgia: FM is a generalized systemic condition that is characterized by widespread aching or pain throughout the body. To be included in the diagnosis of FM, this pain should be located in at least three out of four quadrants of the body or along the entire spine for a minimum of three months.

No one thing: Hi. We do not know what causes either condition, so right now, your guess is as good as mine (or anyone else's). My belief is it's a constellation of causes, not any one thing.