chronic fatigue syndrome 
noun [mass noun]
A medical condition of unknown cause, with fever, aching, and prolonged tiredness and depression, typically occurring after a viral infection.While the authors admit there is no cure, they align chronic fatigue syndrome with other conditions that can be successfully managed without a clear idea of aetiology....
- He was also interested in the contribution of viral infections to chronic fatigue syndrome.
- Narcolepsy has been mistaken for epilepsy, chronic fatigue syndrome, and schizophrenia.