Chronic fatigue syndrome is a multifaceted, long-term illness that impacts on a wide range of systems throughout the body. It causes a wide range of symptoms that might present differently for each person with the condition. The condition is also known as myalgic encephalomyelitis. Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a serious, long-term illness that affects many body systems. Symptoms, Diagnosis and Treatment ME/CFS in Children.