Insomnia Patients are Fatigued But Not Sleepy

Insomnia patients often report fatigue and sleepiness as daytime consequences of insomnia.  A recent study investigated subjective daytime fatigue and sleepiness in insomnia patients. The study sample of 105 healthy sleepers, 671 patients with insomnia, and 602 patients with sleep disorders characterized by excessive daytime sleepiness (EDS) such as sleep apnea.

The results indicated that insomnia patients reported minimal daytime sleepiness levels that were comparable to that observed in healthy sleepers and significantly lower than the EDS group, suggesting that insomnia patients are not sleepy during the day. However, insomnia severity significantly correlated with daytime fatigue. These results suggest that fatigue and sleepiness are two qualitatively different states for insomnia patients. This evidence is consistent with the core feature of insomnia: excessive arousal in the awake system that prevents daytime sleepiness but results in daytime fatigue.