Right or wrong, this appears to be a scientifically framed way of arguing "the problem's in your mind"... dealing with subconscious emotional issues, etc..

Reading between the lines it sounds like you're saying it's acedia, perhaps an extreme form. Acedia appears to be normally distributed in the population, so perhaps those who label it CFS are a couple deviations from the mean. Sure I've felt acedia too after years of working hard at a company I didn't care about with a stressful, long commute. Quitting, traveling for 3 months, exercise, indulging my neglected dating life, and ultimately a career change into a field I cared more about have kept me feeling active and motivated. If I hadn't made those dramatic changes though I very well might have messed myself up long term and developed a more extreme form of acedia.