Sleep-wake behavior in chronic fatigue syndrome.

Observed Findings

• CFS patients reported significantly greater symptom severity, disability, sleep disturbance, and pain sensitivity compared to controls.
• No between-group differences were found in actual sleep duration, sleep pattern, total activity levels, or diurnal cortisol secretion patterns.
• Afternoon activity levels were followed by increased evening fatigue in CFS patients but not in healthy controls.
• Low nocturnal heart rate variability was identified as a biological marker associated with unrefreshing sleep in CFS patients.
• Heart rate monitoring revealed autonomic nervous system differences between groups despite normal cortisol patterns.

Inferred Conclusions

• Circadian rhythm disturbance does not appear to be a primary mechanism of ME/CFS pathology.
• Autonomic nervous system dysfunction, particularly reduced heart rate variability during sleep, may play a significant role in unrefreshing sleep experienced by CFS patients.
• CFS patients show heightened symptom responses to activity, suggesting that activity-related physiology differs from healthy controls despite similar objective sleep and activity patterns.
• Clinical management should focus on activity pacing tailored to individual autonomic responses rather than correcting presumed circadian disorders.

Remaining Questions