Some scientists believe that a virus, stress, or other traumatic condition might trigger the immune system and cause fatigue. No one knows. The main symptom is profound tiredness. People with chronic fatigue syndrome often become exhausted from only light physical activity and must function at a much lower level of activity than they did when healthy. The recovery time varies widely.
Some people eventually make a full recovery, but others seem to get progressively worse.
People with chronic fatigue syndrome often have alternating times of illness and relatively good health. Some improve a bit but never fully recover. No specific diagnostic tests are available. Diagnosis is based on a history of illness that suggests chronic fatigue syndrome and by systematic exclusion of other possible causes of a person's symptoms. However, people of different races and ages have been diagnosed.