PEM, or post-exertional malaise, is a condition characterized by a debilitating and prolonged feeling of exhaustion and physical weakness following even minor physical or mental exertion. It is a common symptom of chronic fatigue syndrome and other chronic illnesses, and can significantly impact an individual’s daily functioning and quality of life. PEM is often accompanied by other symptoms such as brain fog, muscle pain, and flu-like symptoms, and can last for days or even weeks. It is important for individuals experiencing PEM to pace themselves and prioritize rest and self-care in order to manage their symptoms and prevent further exacerbation.