Perception of waking and sleeping: possible implications for the evaluation of insomnia.

Perception of awakening, its connection to electroencephalogram (EEG), and its significance for morning recall were studied in insomniacs and normals. Fourteen insomniacs and 14 age- and sex-matched controls kept a sleep log for 1 week and slept once in the laboratory (standard polygraphy). In addition, actual perception of awakening was measured by a behavioral device. Results suggest that physiological arousal is necessary, but not sufficient, for perception of awakening. Many arousals that are not perceived occur during the first REM-NREM cycle. Insomniacs nearly exclusively perceive those arousals occurring after consolidated sleep (at least 15 min) and at the beginning of interrupted sleep intervals. It is suggested that insomniacs perceive these intervals as continuous wakefulness and have difficulty in perceiving short-lasting sleep, whereas controls often do not perceive wakefulness at all. The latter may be a sleep-protecting mechanism. Number and correlation suggest that recalled awakenings are exactly those perceived. The connection between physiological and experimental subjective data is discussed.