Real illness

Discussing whether something is a real illness can mean many different things, including:
 * whether an illness actually exists, or if the name is used to refer to unrelated symptoms
 * whether the illness is better accounted for by a different diagnosis
 * whether the illness symptoms are clinically significant, or if the person is a hyperchondiac or one of the "worried well" experiencing normal bodily sensations
 * whether an illness is physical (organic) rather a than psychosomatic illness or a mental illness
 * whether the illness is a legitimate, recognized illness, good example it is listed in a diagnostic manual
 * whether an illness is generally recognized by other physicians

ME/CFS
ME/CFS is recognized as a real illness because;
 * it has a collection of symptoms which are linked by a disease process, and medical abnormalities have been found which are not present in healthy people.
 * it has been in the World Health Organization's diagnostic manuals since 1969
 * it is classified as a physical, neurological disease by the World Health Organization, and is regarded as a serious physical disease by the CDC and the UK's National Health Service.
 * symptoms cannot be fully explained by any other illness