Myalgic encephalomyelitis (ME) or chronic fatigue syndrome (CFS) is a long term (chronic) neurological condition that affects the nervous and immune systems. People with ME/CFS experience severe pain and fatigue associated with post-exertional malaise (PEM). This is when the body is not able to recover after using even small amounts of energy. This fatigue feels very different from ordinary tiredness. It might take a day or 2 to kick in after physical, mental, or emotional exertion. ME/CFS affects more women than men, can affect children and adults of all ages and from all social and ethnic groups. It doesn't go away with sleep or rest and affects everyday life. It can sometimes be diagnosed as post viral fatigue syndrome (PVFS).