Short-Term Stability and Night-to-Night Variability of Sleep Parameters in Nightmares Comorbid with Chronic Insomnia Disorder Across Multiple Nights of Polysomnography.

Nightmares are associated with abnormal sleep above and beyond REM disruption, as sleep continuity was the primary aspect in which poor stability and group differences emerged. The greater inability to fall asleep and instability of sleep fragmentation in those with comorbid insomnia/nightmares compared to chronic insomnia alone may be attributed to the impact of pre-sleep anticipatory anxiety and nightmare-related distress itself.