SUMMARY Dream content in NREM and REM sleep correlates with the subjective experience of having slept immediately before awakening. The estimation of depth of sleep depends on the quality of the NREM sleep stages. The presence of dreaming in a given sleep stage is more important for the subjective experience of having slept than the duration of the sleep episode before the awakening. Neurotic insomniac patients more often deny mental activity when awoken from NREM and REM sleep, than do healthy subjects. These data suggest that spontaneous awakenings in different sleep stages, especially in the first sleep cycle, correlate with the insomniac's tendency to underestimate sleep duration and qualit