Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a poorly understood disease that causes exhaustion, sleep problems, thinking problems, and pain throughout the body. There is not yet a cure for ME/CFS. But treating the symptoms and keeping a low-key pace help improve daily life. Some people have severe fatigue and other symptoms for many years. Another name for this condition is systemic exertion intolerance disease (SEID).