A complex, chronic disorder characterised by profound, persistent fatigue unrelieved by rest, often accompanied by cognitive difficulties, muscle pain, and post-exertional malaise, abbreviated ME. Frequently discussed alongside chronic fatigue syndrome, its causes remain unclear, with viral triggers, immune dysfunction, and autonomic abnormalities all investigated. No single diagnostic test exists; diagnosis rests on clinical criteria after excluding other conditions. Various food supplements are marketed with claims of benefit, but evidence is limited, and management focuses on pacing activity, sleep hygiene, and symptom relief. Research continues into the condition’s biological basis and effective treatments.