I'm sure people wonder the same thing so I have some research:
Fibromyalgia (FM) is a real and sometimes disabling condition that was first recognized and named by doctors of rheumatology, probably because it is characterized by widespread chronic pain and stiffness, numerous chronic tender points (more than 11 of 18) and chronic fatigue with exertion intolerance reminiscent of arthritis and autoimmune disease. Other typical symptoms include disordered or unrefreshing sleep patterns, headaches, mood or cognitive complaints (such as "brain fog"), irritable bowel syndrome, and other types of autonomic nervous system dysfunction. Symptom flares occur with increased exertion, systemic infections, soft tissue injuries, lack of sleep, cold exposure, and psychological stressors. Related symptoms and syndromes include restless leg syndrome, irritable bowel syndrome, irritable bladder syndrome, migraine headaches, multiple chemical sensitivities, neurally mediated hypotension, cognitive dysfunction, cold sensitivity, unexplained dizziness, and others. Strangely enough, as we learn more about it, we discover that Fibromyalgia is actually different than arthritis, because it doesn't cause visible destruction of joints or definite inflammation and autoimmunity on blood tests. Instead, there seems to be a disturbance of the central nervous system, resulting in increased pain sensitivity and abnormal central pain processing. which in turn contributes to more pain, tightness and spasm of the tension bearing muscles, connective tissues and associated areas of the brain. Substance P, a neurotransmitter that causes and is a sign of pain, is elevated in spinal fluid of patients with Fibromyalgia. Fibromyalgia typically strikes women three times more often than men, with a median age of 40-50, either definite or gradual in onset, often following periods of emotional stress, and sometimes associated with infection, hormone shifts such as menopause, surgery, or mechanical trauma. The prevalence is thought to amount to 20 cases per 1,000 population, or 3.4% women and .5% of men, obviously much more common than Chronic Fatigue Syndrome. There is an increasing incidence with age, with prevalence reaching 23% in people over 70 years of age. Our understanding of Fibromyalgia is growing, but the official case definition originally published by the American College of Rheumatology and the Arthritis Foundation, is accepted by all knowledgeable specialties of medicine.