Chronic fatigue syndrome (CFS) is a complicated disorder characterized by extreme fatigue that may worsen with physical or mental activity, but doesn't improve with rest. Although there are many theories about what causes this condition — ranging from viral infections to psychological stress — in most cases the cause is still unknown.
Because its symptoms are difficult to measure, CFS wasn't widely accepted as a real medical condition for several years. Today, however, doctors and researchers agree that this chronic condition should be taken seriously.
Although an underlying cause often isn't found, effective treatments for the signs and symptoms of CFS are available. Many people recover from chronic fatigue syndrome over time.