Sleep onset latency

Overview
In sleep science, sleep onset latency (SOL) is the length of time that it takes to accomplish the transition from full wakefulness to sleep, normally to the lightest sleep stage non-REM.

Daytime tests, such as the MSLT, measure sleep onset latency as an indication of excessive daytime sleepiness (EDS). A sleep onset latency of 15-25 minutes in a person's biological daytime is considered normal. A shorter latency is likely a sign that a person suffers from sleep deprivation. A sleep onset latency of less than five minutes indicates either very unhealthy daytime sleepiness or one of several sleep disorders, for example narcolepsy. A long SOL at bedtime can be an indication of a sleep disorder, including but not limited to insomnia.