a debilitating medical condition without an apparent cause, characterized by prolonged severe fatigue, muscle pain, impaired memory, etc.
See chronic fatigue syndrome in American Heritage Dictionary 4
noun Abbr. CFS
A syndrome characterized by debilitating fatigue and a combination of flulike symptoms such as sore throat, swollen lymph glands, low-grade fever, headaches, and muscle pain or weakness. Also called chronic fatigue immune dysfunction syndrome.