For decades, chronic fatigue syndrome (CFS) has been recognized as a condition that is exactly as its name suggests: chronic (long-lasting) problem with fatigue (tiredness, lack of energy). It has been difficult for people with CFS to receive proper diagnosis and treatment, since the cause or causes are unknown, and there have been no lab tests or other objective studies to identify it with certainty. The condition is now known as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS,