Sleep Onset Latency: What Is It?

Sleep onset latency, or SOL, is a key component in determining a range of sleep disorders. It’s a term sleep specialists use for “the time to first sleep entry episode,” according to the National Institutes of Health’s Interactive Textbook on Clinical Symptom Research. In other words, sleep onset latency defines how long it takes you to drift off to sleep after your head hits the pillow.

SOL at Home

At home, it’s difficult to measure sleep onset latency with precision—you’ll usually only notice SOL if it’s a problem. If you lie down, relax for a few minutes, and then drift off gently to sleep and stay asleep, your SOL indicates that you have a healthy relationship with sleep. If you fall asleep the second your head hits the pillow—or if you toss and turn for an hour or more before falling asleep—your SOL is telling you there may be a problem. We’ll cover this in more depth next time.

SOL in the Lab

In sleep laboratory settings, an EEG can measure brain waves to determine precise moments that brain activity shifts from sleeping to waking. The transition from wakefulness to sleep isn’t sharp and clearly defined, however. Rather, brain waves shift slowly, indicating a “continuum” between wakefulness and sleep.

Most labs pinpoint “sleep” as the moment when 30 seconds have passed since Stage 2 sleep began. Some use 30 seconds after entry into Stage 1, but Stage 1 is considered an “in-between” phase between wakefulness and sleep by most sleep specialists. In any case, official medical sleep latency numbers use the time between lying down to sleep and a pre-determined definition of sleep onset in order to create a replicable measurement.

What’s your sleep onset latency like? Do you fall asleep immediately? Stay awake too long? Or do you feel like you have a healthy relationship with sleep?

Author Bio: +Michelle Gordon is a sleep expert who researches and writes about sleep and health, and is an online publisher for the latex mattress specialist Latexmattress.org.