What is ME/CFS?

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome is classified by the World Health Organization as a neurological condition.

ME/CFS is a serious, complex and disabling neuroimmune condition that affects every system in the body, significantly reducing functional capacity.

Key Symptom: Post-Exertional Malaise

Post-exertional malaise (PEM) or post-exertional neuroimmune exhaustion (PENE) is a pathological loss of energy and worsening of symptoms following minimal physical, mental or emotional effort, or other triggers. The onset of PEM may be immediate or delayed by several hours or days. Recovery is prolonged and may take days, weeks or months.

When people with ME/CFS push themselves to use more than their available energy reserves, the loss in functional capacity is inevitable and cannot be reversed by a long rest or a good night's sleep.

People often struggle to describe this loss of energy, weakness and exacerbation of symptoms. They may use words like crash, payback, debilitating exhaustion.

Other common symptoms

  • Fatigue: unlike normal tiredness, this is a profound and incapacitating lack of energy.
  • Autonomic dysfunction: inability to stand or sit up, air hunger, dizziness, and more.
  • Neurocognitive dysfunction: problems with concentration, information processing, memory, physical tasks, and more.
  • Immune dysfunction: swollen and/or tender lymph nodes, sore throat, and more.
  • Sleep dysfunction: non-restorative sleep, altered sleep patterns, and more.
  • Gut: nausea, irritable bowel, food intolerances, and more.
  • Pain: in muscles and joints, headache, and more.
  • Sensitivities: light, noise, movement, medications, chemicals, and more.

Use the links to learn more about each symptom, including how it is experienced in ME/CFS, and common approaches to treatment and management of that symptom.

...patients with this illness experience a level of disability that’s equal to that of patients with late-stage AIDS, patients undergoing chemotherapy, or patients with multiple sclerosis.

Prof Nancy Klimas MD, AIDS and ME/CFS specialist and researcher, University of Miami, Press Conference, 2006

Levels of severity

What is ME/CFS?  page Whitney
Photo courtesy Janet Dafoe
Whitney Dafoe, healthy and with very severe ME/CFS
  • Mild: at least 50% loss of function
  • Moderate: mostly housebound, requiring support with some activities of daily living
  • Severe: housebound and often bedbound, requiring assistance with personal care
  • Very severe: totally bedbound; unable to eat, drink or speak

For people with ME/CFS, even basic activities of daily living (ADLs) such as toileting, bathing, dressing, talking, and reading can trigger PEM.

The severity of symptoms depends on the severity of the illness. For example, noisy environments may be painful for some with mild illness, while even a whisper might induce a paralysis for some whose illness is very severe.


Despite much ongoing research, the cause of ME/CFS is unclear. The most commonly reported precipitating factor is an infection. ME/CFS is a complex disorder and may have a variety of triggers, including exposure to toxins, severe physical or emotional trauma, or a combination of these or other factors. There are some indications that there may be a genetic predisposition.

Course of the illness

Most people with ME/CFS will have been ill for months or years before a diagnosis is made. Prognosis is generally better for those who are diagnosed early and receive appropriate management.

The severely debilitating symptoms of ME/CFS prevent people from engaging in pre-illness levels of activity for years and often decades. While some improve with appropriate management, few are able to return to their pre-illness level of functioning, and some deteriorate over time. Symptoms fluctuate, with temporary or permanent exacerbations.

Who is affected?

  • In Australia up to 250,000 people have ME/CFS, including an estimated 11,000 South Australians.
  • 25% of cases are severe or very severe.
  • ME/CFS affects all age groups, including young children.
  • Peak ages of onset are 10-19 and 30-39 years.
  • Fewer than 15% of people with ME/CFS are able to work even part-time.
  • ME/CFS affects four times more women than men.

Last edited: 28 April, 2023