CFS (Chronic Fatigue Syndrome) is a disorder of unknown cause that lasts for prolonged periods and causes extreme and debilitating exhaustion as well as a wide range of other symptoms such as fever, headache, muscle ache and joint pain, often resembling flu and other viral infections. Also known as Chronic Fatigue and Immune Dysfunction Syndrome (CFIDS), Chronic Epstein-Barr Virus (CEBV), Myalgic Encephalomyelitis (ME), “Yuppy Flu” and other names, it is frequently misdiagnosed as hypochondria, psychosomatic illness, or depression, because routine medical tests do not detect any problems.