Fibromyalgia is a mysterious disorder of unknown cause characterized by widespread pain, abnormal pain processing, sleep disturbance, fatigue and often psychological distress. According to the CDC, fibromyalgia affects an estimated 5 million adults. Dr. Sean Mackey, assistant professor of anesthesia at the Stanford University Medical Center, discusses our current understanding of this cryptic disorder: its pathology, diagnosis and treatment. From the Series:The Stanford University Medical Center Health Hour