The Nightmares of Sleep Apnea: Nightmare Frequency Declines with Increasing Apnea Hypopnea Index

The nightmare is defined as a disturbing mental experience that generally occurs during REM sleep and often results in awakening.1 The typical nightmare is a coherent dream sequence that seems real and becomes increasingly more disturbing as it unfolds. The negative emotions characterizing nightmares usually involve anxiety, fear or terror but also include anger, rage, embarrassment, and disgust. Nightmares have also been differentiated from other intense dreams by the characteristic of dream imagery expressed as an unmitigated perception of external reality.2,3 Nightmare content most often focuses on imminent physical danger to the individual (e.g., threat of attack, falling, injury, death) but may also involve aggression toward others, potential personal failures, and other distressing themes such as suffocation. Dream and nightmare recall frequency can be assessed by retrospective and longitudinal questionnaires, nocturnal REM sleep, awakenings, and by diaries. Studies designed to compare different assessments of dream and nightmare recall have generally found a remarkably high correlation between assessment methods for dream recall frequency with questionnaire reports of dream and nightmare recall having been shown to have longitudinal consistency and retest reliability.4,5 Five to eight percent of the general population reports a current problem with nightmares.6,7 In some clinical populations including insomniacs, nightmares are reported at much higher frequencies.8–10 Among individuals presenting at sleep laboratory facilities, nightmares are reported as a salient complaint by 16% of patients and positively correlated with reported lower sleep quality, and worse sleep and medical outcomes.11 BRIEF SUMMARY Current Knowledge/Study Rationale: This study was designed in an attempt to clarify the association of reported nightmare recall with polysomnographically defined OSA in the sleep laboratory population. This is among the first large studies to address both reported dream and nightmare recall frequency in a polysomnography evaluated study population including a high percentage of patients with severe OSA. Study Impact: Sleep laboratory patients with more severe OSA, as based on higher AHI, report significantly lower nightmare frequency, indicating that OSA suppresses the cognitive experience of nightmare recall, an effect occurring independently of OSA effects on reported dream recall frequency. This effect is likely secondary to OSA induced REMS suppression emphasizing differences between nightmares that are REMS associated parasomnias, and dreaming that can be reported from all stages of sleep.