Myalgic encephalomyelitis, also called chronic fatigue syndrome or ME/CFS, is a complex long-term condition. Its central feature is post-exertional malaise, a worsening of symptoms after physical, cognitive, emotional or social activity that may be delayed and can last for days or longer.
Core symptoms
- fatigue that substantially reduces previous activity and is not relieved by rest
- post-exertional malaise after activity
- unrefreshing sleep or a changed sleep pattern
- problems with thinking, concentration or memory, sometimes called brain fog
Other symptoms may include pain, headaches, flu-like feelings, sensitivity to light or sound, and dizziness, palpitations or faintness when standing. Severity varies. Some people remain able to work with adjustments, while others are housebound or bedbound and need substantial care.
Diagnosis
There is no single diagnostic test. A clinician assesses the pattern and duration of symptoms, examines the person and uses appropriate tests to rule out other causes such as anaemia, thyroid disease, sleep disorders, infection or another neurological, cardiac or inflammatory condition. NICE advises considering ME/CFS when the characteristic symptoms persist and are not explained by another condition, with confirmation after three months.
Energy management
Energy management aims to keep activity within the person’s current limits and reduce post-exertional worsening. Activity includes physical movement as well as mental, emotional and social effort. Plans should be flexible and individually agreed, with rest incorporated before symptoms escalate.
Fixed programmes that require activity to increase by predetermined amounts, often called graded exercise therapy, should not be offered as a treatment for ME/CFS. Exercise advice intended for healthy people or other conditions may worsen symptoms if post-exertional malaise is not considered.
Treatment and support
There is currently no curative treatment. Care may include support with sleep, pain, nausea, orthostatic symptoms, nutrition, mobility, education or employment adjustments and mental wellbeing. Cognitive behavioural therapy may be offered to help a person manage the impact of living with ME/CFS, but it is not a cure and does not imply that the illness is psychological.
When to seek further help
Seek medical assessment for persistent, unexplained fatigue or a clear change in symptoms. Urgent help is needed for severe breathing difficulty, chest pain, fainting with delayed recovery, new neurological symptoms, inability to drink, signs of severe dehydration or immediate risk of self-harm.
Sources
Reviewed: 28 August 2026