Chronic Fatigue Syndrome (CFS), also known as Myalgic Encephalomyelitis (ME/CFS), is a long-term condition that causes overwhelming tiredness that doesn’t get better with rest. A hallmark feature is post-exertional malaise, where even light physical or mental activity can make symptoms much worse, sometimes for days. People often also experience poor sleep, trouble concentrating or remembering things (“brain fog”), and dizziness when standing. The exact cause isn’t known, and while there’s no cure, treatments focus on managing symptoms and pacing activities to improve quality of life.