Nightmares and oxygen desaturations: is sleep apnea related to heightened nightmare frequency?

In the 19th century, several authors held the view that nightmares are caused by oxygen shortage. The present study was designed to study nightmare frequency in patients with obstructive sleep apnea syndrome and its relationship to respiratory parameters. A brief questionnaire was administered to 323 patients with sleep apnea syndrome before their first laboratory night. The reduction in nightmare frequency in the sleep apnea group was explained by the reduced dream recall frequency. Despite some illustrative examples of a correlation between oxygen desaturation and dream content, the respiratory parameters as measures of sleep apnea syndrome severity did not correlate substantially with nightmare frequency. Psychiatric comorbidity and an intake of psychotropic medication were associated with heightened nightmare frequency in this sample. It must be concluded that the oxygen hypothesis did not play a major role in explaining the occurrence of nightmares. As this might be partly explained by adaptation to the nightly desaturation periods, it will be fruitful to apply experimental procedures that interrupt airflow during (rapid eye movement) REM sleep for short periods in a systematic way without the knowledge of the sleeper and to then study their effects on dream content. Some patients reported a correlation between daytime stressors and nightmares, which is in line with modern etiological models of nightmares.