What Is the Moment of Sleep Onset for Insomniacs?

Subjective estimates of sleep latency were compared with three EEG-assessed measures of sleep onset: (a) the traditional one, i.e., the first epoch that is scored as stage 2 sleep; (b) the beginning of the first 15 min of uninterrupted stage 2 sleep; and (c) the beginning of the first 30 min of uninterrupted stage 2 sleep. A total of 56 insomniacs and 10 good sleepers were studied for 3 nights each in the laboratory. The traditional measure of sleep latency agreed best with the subjective estimates of good sleepers. Most insomniacs, however, were best able to estimate their sleep latency when the 15-min criterion was used. We suggest that for most insomniacs the subjective experience of being asleep occurs later in the EEG-defined transition from waking to sleeping than it does for good sleepers.