Chronic fatigue syndrome (CFS) is also known as Myalgic Encephalomyelitis (ME).
CFS is a tiredness that affects everyday life and does not improve with sleep or rest. ME is the commonly used term although as Myalgia refers to muscle pain and Encephalomyelitis is an inflammation of the brain and spinal cord some believe this does not sufficiently describe all the symptoms. Long-term tiredness or chronic fatigue can exist without the inflammation. Hence the medical profession tend to use the term CFS.
It is more common in women than men and usually develops in the early twenties to mid-forties.