Figuring Out Fibromyalgia Perplexing Pain and Fatigue An unknown cause. A difficult diagnosis. No known cure. No wonder people with fibromyalgia syndrome, or FMS, can feel perplexed, under attack and isolated. FMS brings fatigue that drags you down and persistent pain that may render you nearly helpless. Researchers have been working to understand what fibromyalgia is and are making progress in developing treatments for the debilitating syndrome.