In the journal Sleep, K Rahman et al published a study that assessed the relationship of sleep-wake behavior and chronic fatigue syndrome (CFS). Patients with CFS usually report unrefreshing and restless sleep. To date, scientists have not been able to figure out what makes CFS patients experience the subjective sleep disturbances. In addition, sleep studies have not confirmed objective sleep disturbances in patients with CFS, meaning that there is no evidence that CFS results from a sleep disorder. Researchers do feel that changes in sleep patterns and activity levels can maintain the symptoms of CFS.
This study attempted to determine if circadian rhythm disturbances could be responsible for the fatigue and unrefreshing sleep reported in CFS patients. The results, though, showed no differences in recordings of sleep pattern, sleep duration, daytime activity, or cortisol secretion (a marker of circadian rhythm) between CFS patients and control subjects. The authors concluded that a disruption in circadian rhythm is not associated with CFS.
Interestingly, despite no differences in objective sleep measures, all of the CFS patients in this study reported poor sleep quality. One finding that was different between CFS patients and the control subjects was a loss of vagal modulation of heart rate in CFS patients, which indicates a state of increased sympathetic arousal. Think of vagal modulation (or parasympathetic system) as the brakes of a car and the sympathetic system as the accelerator - thus, in CFS patients, the brakes do not work and the accelerator is going unchecked. There are studies that suggest that normal vagal modulation is needed to make sleep restorative. Therefore, the decrease in vagal modulation could be a biological explanation for the poor sleep quality reported by CFS patients.
It would be interesting to see if medications that increase vagal tone have been reported to make sleep more refreshing. If anyone knows of such reports, put it in a comment here.