It should be explained that there are a number of different names for what is an illness of uncertain cause affecting many thousands of people. Currently it is estimated that some 250,000 people in Britain are affected by this illness.

• Myalgic Encephalopathy or "ME" (a term which The ME Association feels is more appropriate than the original, Myalgic Encephalomyelitis)
• Chronic Fatigue Syndrome or "CFS"
• Post-Viral Fatigue Syndrome or "PVFS"
• Chronic Fatigue Immune Dysfunction Syndrome or "CFIDS"

All types of people at all ages are affected. Severe and debilitating fatigue, painful muscles and joints, disordered sleep, gastric disturbances, poor memory and concentration are commonplace. In many cases, onset is linked to a viral infection. Other triggers may include an operation or an accident, although some people experience a slow, insidious onset.