Severe myalgic encephalomyelitis or chronic fatigue syndrome

Severe myalgic encephalomyelitis or severe chronic fatigue syndrome or severe ME/CFS is a serious and extremely disabling neurological disease. Severe ME/CFS causes a very severe level of disability.

NHS definition
Severe ME/CFS

People with severe ME/CFS are unable to do any activity for themselves or can carry out minimal daily tasks only (such as face washing or cleaning teeth). They have severe cognitive difficulties and may depend on a wheelchair for mobility. They are often unable to leave the house or have a severe and prolonged after-effect if they do so. They may also spend most of their time in bed and are often extremely sensitive to light and sound.

The UK's National Health Service definition of severe and very severe ME/CFS can be found within the 2021 NICE guidelines.

International Consensus Criteria


Fluctuating level of symptoms
Symptoms may fluctuate in people with ME/CFS, but those with severe ME/CFS will not have any days with only mild symptoms, and regular work outside the home, even if part-time, will be impossible.

Some people with severe ME/CFS will be able to leave home at times, but will be dependent on a wheelchair or mobility scooter.

Invisible illness
ME/CFS is known as an invisible illness due to the lack of obvious physical signs of illness. However, the severity of severe ME/CFS may make their illness more obvious, for example a person in their 20s needing a mobility scooter or wheelchair, or someone in their 30s being unable to play with their young children, or relying on an elderly parent for personal care.

People with severe ME/CFS may struggle to explain the severity of their illness: being "unable to get out of bed" may mean literally needing to be lifted out of bed by another person due to severe muscle weakness.

Activities that are usually seen as relaxing or enjoyable may be strenuous or totally impossible with severe ME/CFS, for example having a bath, watching a movie, or talking to a friend by phone. Being unable to do everyday activities may be confused with a lack of interest in things and withdrawing from other people, which are symptoms of depression, but with ME/CFS there is no lack of interest but a lack of ability instead.