Anecdotally I used to think that sufferers of Chronic Fatigue were suffering from psychological issues. Earlier this year I was diagnosed with EBV that led to a post viral illness (the first step in EBV becoming Chronic Fatigue). I saw a number of medical specialists and I would them that their diagnosis doesn't make sense. I'd never even heard of illness leading to Chronic Fatigue. Luckily I recovered, or am nearly 100% recovered, but it changed my mind on the illness.