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

STUDY OBJECTIVES The purpose of this study was to examine the degree of short-term stability of polysomnographic (PSG) measured sleep parameters and the overall differences between individuals with comorbid nightmares and insomnia compared to those with chronic insomnia disorder alone or good sleeping controls across four nights in the sleep lab.

Methods: A total of 142 good sleeping controls, 126 chronic insomnia alone and 24 comorbid insomnia/nightmare participants underwent 4 consecutive nights of 8-hour PSG recordings. Outcomes included sleep continuity, architecture, and REM-related parameters across nights 1 through 4. Intraclass correlation coefficients with mixed-effect variances and repeated-measure analysis of covariance were used, respectively, to determine short-term stability as well as between-subjects and time-by-group interaction effects.

Results: Wake after sleep onset and stage 1 showed "poor stability" in the comorbid insomnia/nightmare group compared to "moderate stability" in the good sleeping controls and chronic insomnia alone group. Significant between-group effects (all ps<0.05) showed that the comorbid insomnia/nightmare group took longer to fall asleep and had a greater first-night-effect in stage 1 compared to good sleeping controls and chronic insomnia alone group; in addition, the comorbid insomnia/nightmare and insomnia alone groups slept shorter, yet had fewer awakenings and REM periods, compared to the good sleeping controls.

Conclusion: 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.