As the name suggests, people with chronic fatigue syndrome (CFS) — also sometimes known as myalgic encephalomyelitis (ME) — feel very tired and exhausted most of the time.
The fatigue is not relieved by rest and is often much worse after physical or mental activity.
The main symptom of chronic fatigue syndrome is extreme, overwhelming tiredness or fatigue. The fatigue is both physical and mental and does not improve with rest or sleep.