Since poor sleep quality is a core symptom of CFS I can't help wonder if sleep is the underlying component. I think we've all underestimated the critical nature of sleep in immune, metabolic, stress, cognitive aspects, etc. It's also hard to self-assess the quality of your sleep, eg. clock-time at each phase, central apnea events, 02 saturation, noise/ light/ movement disturbances while you are asleep, etc.