Fig. 3.

Loss of regulatory association between sleep quality and nocturnal cortisol secretion among patients with chronic fatigue syndrome and/or fibromyalgia compared to healthy controls. PSQI, Pittsburgh Sleep Quality Index global score, in which higher scores = worse sleep quality over the previous month. Among healthy controls, worse sleep quality is associated with significantly lower levels of the parameter reflecting the intercept in the dynamic model. This parameter reflects non-ACTH influences on cortisol and is primarily correlated with the level of cortisol during the circadian nadir in the early evening. See Tables 3 and 4.