What is M.E.?

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What does M.E. feel like?

What is M.E.?

Myalgic Encephalomyelitis (M.E.) is a long-term (chronic), fluctuating, neurological disease that causes symptoms affecting many body systems, more commonly the nervous and immune systems. M.E. affects an estimated 250,000 people in the UK, and around 17 million people worldwide.

People with M.E. experience debilitating pain, fatigue and a range of other symptoms associated with post-exertional malaise, the body and brain’s inability to recover after expending even small amounts of energy.

Not everyone will experience the same symptoms so it's important not to compare someone who has M.E. to another person who has the illness. People with M.E. can vary enormously in their experience of the illness, and also how long their symptoms last. Some make good progress and may recover, while others can remain ill for a number of years and may not get better. Some people find that they don’t go back completely to the way they felt before they became ill, but they do recover sufficiently to lead happy and fulfilling lives. This is similar to many other chronic illnesses.

This section gives you more information about M.E., including possible causes and sub-groups within the disease.

Our booklet, Newly diagnosed with M.E., has advice for you and your GP, facts about M.E., guidance to help you be an active partner in your own care, suggestions for questions for you to ask your GP and information about existing guidelines.

What does M.E. feel like?

Sam tells us:

“It’s like having glandular fever, taking your glandular fever on an all-night drinking binge, then taking your glandular fever and your hangover and doing a 30km forced march over the Brecon Beacons. The way you would feel at the end of that is how it feels to have M.E. every day. It is like being on a carousel: you have ups and downs but you can never get off.”

Another Action for M.E. supporter says:

“I feel like I wake up with a mattress on me most mornings. When I wake up with post-exertional malaise, there is an elephant sitting on the mattress. He stays there for days. He steals my words and fills my brain with wet cotton wool and wraps his trunk around my neck, so I struggle to swallow.”

Degrees of severity

The National Institute for Health and Care Excellence (NICE) acknowledges that the physical symptoms of M.E. can be as disabling as multiple sclerosis, systemic lupus erythematosus, rheumatoid arthritis, congestive heart failure and other chronic conditions. Other research shows that people with M.E. score lower overall on health-related quality of life tests than most other chronic conditions (Hvidberg et al, 2015).

The October 2021 NICE guideline for M.E./CFS describes four levels of severity of M.E./CFS, making it clear that "individual symptoms vary widely in severity and people may have some symptoms more severely than others. The definitions below provide a guide to the level of impact of symptoms on everyday functioning."

  • People with mild M.E./CFS care for themselves and do some light domestic tasks (sometimes needing support) but may have difficulties with mobility. Most are still working or in education, but to do this they have probably stopped all leisure and social pursuits. They often have reduced hours, take days off and use the weekend to cope with the rest of the week.
  • People with moderate M.E./CFS have reduced mobility and are restricted in all activities of daily living, although they may have peaks and troughs in their level of symptoms and ability to do activities. They have usually stopped work or education, and need rest periods, often resting in the afternoon for 1 or 2 hours. Their sleep at night is generally poor quality and disturbed.
  • People with severe M.E./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.
  • People with very severe M.E./CFS are in bed all day and dependent on care. They need help with personal hygiene and eating, and are very sensitive to sensory stimuli. Some people may not be able to swallow and may need to be tube fed.

Even in its so-called mildest form, M.E. can have a significant impact on an individual’s life, and not just on their health. A lack of understanding and awareness about M.E. means patients can experience disbelief, and even discrimination, from friends, family, health and social care professionals and employers. Action for M.E. is here to help.

Chronic fatigue syndrome (CFS)

Within the NHS, a diagnosis of chronic fatigue syndrome (CFS) or CFS/M.E. is often given. This can make it confusing for many.

In February 2015, the Institute of Medicine in the United States recommended changing the name to systemic exertion intolerance disease, or SEID. This has not been universally adopted.

Action for M.E. uses the terms M.E., CFS and M.E./CFS because we do not wish to withhold support from those who have been given a diagnosis of CFS, as opposed to M.E. We recognise that it is quite possible that M.E./CFS may be an umbrella term for a number of illnesses. Therefore, it is critical that there is more biomedical research to further investigate and validate our understanding and increase knowledge of the different sub-groups (phenotypes) of M.E. and/or CFS.

What causes M.E.?

The causes of M.E. are still being investigated. Emerging evidence indicates that there are likely to be a number of factors involved and that there may be a number of different types or sub-groups of the illness.

There is evidence that certain infections can trigger the illness. Many are viruses but M.E. may be triggered in other ways.

Common viral triggers include glandular fever or Epstein-Barr virus (EBV). Other herpes viruses such as herpes simplex, VZV (causes chickenpox/shingles), HHV-6 and CMV, may sometimes trigger M.E., as can viral meningitis or labyrinthitis, commonly caused by enteroviruses, gastroenteritis, Hepatitis A, B and C infection, and in Australia, Ross River virus.

This means we face the possibility, being raised by our medical advisors, researchers we work with and international experts, of a spike in post-Covid illnesses – including M.E.

Non-viral triggers include toxoplasma, brucella, salmonella, tuberculosis, Q fever, and Lyme disease. However, there is no clear evidence that M.E. is a form of persistent, chronic infection – it may be a consequence of infection.

In a very small number of people, the trigger may have been an immunisation, given perhaps when they were already unwell, or a physical trauma, such as a road accident, operation, radiotherapy or chemotherapy, or whilst rare, it is suspected that a very few cases may be triggered by certain toxic substances.

One big outstanding question is whether emotional stressors can be a trigger. Studies are not clear, some suggesting a link and others not. It is very unlikely that stressful life events, such as bereavement, can trigger M.E. on their own.

Often it isn’t possible to find out exactly what caused your illness – but you can still improve your symptoms, despite not knowing the exact trigger.

Other factors

There are likely to be a number of factors involved. It sometimes affects more than one family member. The reasons for this are being investigated but some studies indicate that genes can play a part, as can environmental influences.

It is not clear why some people get M.E. while others recover; some fully and others to a degree. Around one in four people remain severely ill for many years. People who get M.E. may be vulnerable genetically, or their recovery after an infection could be affected by, for example, trying to return to work too soon, doing vigorous exercise, or experiencing major stresses.


There is growing evidence from experts in the field of M.E. that a number of sub-groups exist within M.E., on the basis that individuals within these sub-groups differ in terms of their illness experience and the course their illness follows over time.

The likelihood of multiple sub-groups within M.E. most probably explains the huge variation observed by doctors in the progression of the illness and underlines the difficulty of making a prognosis. The experience of doctors specialising in M.E. is that some people recover completely (the rate is higher for young people) and that others people improve, often significantly, over time. However, some remain very ill, often bedbound and/or housebound for many years.

Identification of sub-groups will, it is hoped, help doctors to improve and personalise treatments for managing the symptoms of M.E.