There is an absolute correlation between Fibro and Cortisol levels. I'm read a very current book written by doctors called "Fibromyalgia and Chronic Myofascial Pain, Second Edition". It talks about the HPA axis (Hypthalmus, Pituitary Gland, Adrenal Glands). When the two glands in the brain - Hypothalmus, Pituitary, send out signals to the adrenal glands (which sit on the kidneys), the message is all messed up. The result is that the adrenals then pump out way more cortisol than is needed.
That is why so many of us have anxiety disorders! Cortisol is the "fight or flight" hormone. When you have an adrenalin rush, that is the cortisol or adrenalin working. Anxiety and cortisol is very closely linked.
This is another reason why Prednisone is so bad for anyone with Fibromyalgia. We already have too much cortisol in our bloodstream. When we add prednsione to the mix we are on overload. The result = pain. I have a terrible time balancing my prednisone doses. I have to be on prednisone because of my lupus. For me it's a catch 22.
So the best thing we can do for ourselves is manage our stress levels. Keep the cortisol down. Easier said than done!