Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a severe, long-term illness that affects many body systems. People with Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) are often not able to do their usual activities. At times, Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) may confine them to bed. People with Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) have severe fatigue and sleep problems.