Chronic Fatigue Syndrome (CFS), also referred to as Myalgic Encephalomyelitis (ME/CFS), is a complex, long-term medical condition characterised by extreme fatigue that is not explained by any underlying disease and does not improve with rest. It is recognised by the World Health Organisation and classified as a neurological condition.
The exact cause remains unclear, though research points to a combination of factors, including viral or other infections that trigger the onset, immune dysregulation, mitochondrial dysfunction, autonomic nervous system abnormalities, and oxidative stress. Many patients report that their symptoms began after an acute illness, sometimes a viral infection, sometimes something more difficult to pinpoint.
What makes CFS particularly difficult is that it is not visible and not easily measurable. Blood tests often come back normal. Patients can look well whilst functioning at a fraction of their previous capacity.
Common long-term consequences of CFS include:
- Persistent, debilitating fatigue lasting six months or more, not relieved by rest
- Post-exertional malaise (PEM), a worsening of symptoms following physical or mental activity, often delayed by 12-48 hours
- Unrefreshing sleep, regardless of duration
- Cognitive difficulties, commonly described as brain fog, include problems with memory, concentration, and word-finding
- Orthostatic intolerance, feeling worse when standing upright, sometimes with dizziness or palpitations
- Widespread muscle or joint pain without swelling or inflammation
- Headaches of a new type, pattern, or severity
- Sore throat or tender lymph nodes, often recurring
- Heightened sensitivity to light, noise, or temperature
The severity varies considerably. Some patients manage a reduced version of their previous life. Others are largely housebound or bedbound for extended periods. There is no single test that confirms the diagnosis, and no single treatment that reliably resolves it.