Chronic fatigue syndrome (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 CFS. But treating the symptoms and a keeping a low-key pace help improve daily life. Some people have severe fatigue and other symptoms for many years. Other names for this condition are systemic exertion intolerance disease (SEID) and myalgic encephalomyelitis (ME).