Why do we experience fatigue?

Anne was a mother of two from Norway, she was thirty nine years old. She caught a virus in 1999, from which she never completely recovered. Anne was diagnosed with post viral syndrome (PVFS) at first. This developed into M.E. (Myalgic Encephalomyelitis) or Chronic Fatigue Syndrome. Anne experienced extreme fatigue, IBS (Irritable Bowel Syndrome) and Insomnia. She also became sensitive to sound and light.