The cyclic occurrence of REM periods (sleep characterized by a low voltage, desynchronized EEG pattern, and rapid eye movements)1,3 and the association of these periods with reports of dreaming1,4,6,7,9,10,14 have been well established. With the exception of narcoleptic sleep,5,13 and the sleep of amphetamine addicts subjected to drug withdrawal,12 REM periods do not occur during nocturnal sleep until after the passage of approximately 45 minutes of NREM sleep (periods characterized by EEG sleep spindle and/or δ-activity and the absence of rapid eye movements).
Although reports of dreaming are sometimes elicited on awakenings from NREM sleep, the frequency of such reports is less than the frequency for REM period awakenings, and the quality of these reports is less "dream-like" than the quality of REM period reports.6,14 Therefore, one would expect, upon hearing vivid, well-recalled, thematically organized dreams, that they were experienced during
MARON L, RECHTSCHAFFEN A, WOLPERT EA. Sleep Cycle During Napping. Arch Gen Psychiatry. 1964;11(5):503-508. doi:10.1001/archpsyc.1964.01720290045006