Is Falling Asleep Too Fast a Sign of a Sleep Disorder?

If you can nod off quickly, sleep deeply, nap anytime, or fall asleep anywhere, you may consider yourself the perfect sleeper. But being able to fall asleep fast can actually be a symptom of a sleep disorder. 

This article explains the science of getting sleepy. It also discusses sleep disorders that could leave you feeling sleepy throughout the day.

How Does Sleepiness Occur?

First, it's important to understand how we become sleepy.

While you are awake, your brain produces a chemical called adenosine. As your body uses energy and conducts its normal waking functions, adenosine builds up. The level of adenosine gradually rises the longer we stay awake.

High levels of adenosine create what's called the homeostatic sleep drive. This is sometimes referred to as sleep load or sleep debt. Simply stated, it's the physical need for sleep to restore your body.

For example, if you were awake for 30 straight hours, you would feel extremely sleepy. You would probably fall asleep easily and sleep deeply. You might even sleep longer than you normally do. That's because of the high levels of adenosine in your brain.

Even staying up past your normal bedtime can mean you fall asleep faster because your adenosine levels are up.

When you sleep, your lymphatic system acts like a filter to clear the adenosine from your brain. When you wake up in the morning, the levels of adenosine—and sleepiness—are at their lowest. If you've slept well, you feel refreshed. 

But what happens when these levels are consistently⁠ too high?

How Fast Is Too Fast to Fall Asleep?

You may not know exactly how long it takes you to fall asleep.

First, your long-term memory may not keep track of the time you spend dozing off. As a result, you may feel that you are falling asleep faster than you actually are.

Second, the lightest stage of sleep can be misinterpreted as wakefulness if you are suddenly awakened from it. You may feel as if you were awake longer than you were because you slipped in and out of light sleep.

You're considered "asleep" when your muscle tone relaxes and the electrical waves in your brain slow down. These brain waves are called theta activity. Theta waves occur at a speed of four to eight times per second (hertz). By comparison, electrical waves in an awake, alert brain travel at twice this rate.

That's why people in the lightest stage of sleep don't respond to what's happening in the environment around them.

The time it takes to move from wakefulness to sleep is called the sleep onset latency. It's measured by tracking the electrical activity of the brain. Sleep specialists use an electroencephalogram (EEG) as part of a sleep study, called a polysomnogram. Electrodes are placed on the scalp to measure brain waves and record when various stages of sleep occur.

On average, a person without excessive sleepiness should fall asleep in five to 15 minutes. If it takes longer than 20 to 30 minutes, it could be a sign of insomnia.

In short, you may be falling asleep fast not because you are a "good sleeper" but because you are deprived of the sleep you need.

What Causes Excessive Sleepiness?

The most common cause of sleepiness is sleep deprivation. If you don't get enough hours of sleep to feel rested and to clear away the adenosine, you will fall asleep faster. An average person needs just over eight hours of sleep. Some people may need more or less.

If you fall asleep quickly, take naps, doze accidentally, or sleep in on the weekends, you may be sleep deprived. A little extra sleep may be all it takes to ease your sleep debt.

If you're not getting quality sleep or you wake up often during the night, this can also lead to falling asleep too quickly. Waking up a lot is called sleep fragmentation. Your sleep is literally broken up. The most common cause is sleep apnea.

In people with sleep apnea, breathing stops briefly many times during the night. These breathing problems can wake you up. Sleep apnea is associated with other symptoms, including teeth grinding, snoring, and frequent trips to the bathroom at night. Fortunately, effective treatments exist to restore sleep quality.

Other disorders can fragment sleep as well. One possibility is restless legs syndrome. It causes an uncomfortable feeling that you need to move your legs. Narcolepsy is another possibility. It causes you to slip into sleep without warning during waking hours.

When sleep specialists can't pinpoint exactly why you're so sleepy, it may be diagnosed as idiopathic hypersomnia. That's the medical term for excessive sleepiness with no known cause.

Testing

The simplest way to measure sleepiness is by completing a questionnaire called the Epworth sleepiness scale. If you score higher than 10 on this scale, you probably have excessive sleepiness. The next step may be a formal sleep study.

The multiple sleep latency test (MSLT) can also be used to measure sleepiness. It is sometimes used to check for narcolepsy. In an MSLT, you are given a chance to take 20-minute naps every two hours during a day. 

On the MSLT, falling asleep in less than eight minutes is not considered normal. Sleep specialists record when your rapid eye movement (REM) sleep starts during a nap. If REM sleep starts within 15 minutes in two or more of your naps, you may be diagnosed with narcolepsy.

Summary

Feeling sleepy is the result of the chemical adenosine. It builds up in your brain while you're awake. Sleep resets the adenosine levels.

If you're falling asleep fast, it could be because you're not getting enough quality sleep during the night. You may be sleep-deprived, which could explain the need for naps and the tendency to drift off even when you don't mean to.

Disorders such as sleep apnea, restless leg syndrome, narcolepsy, and other neurological conditions could be the cause. To find out exactly what the problem is, a sleep specialist could give you sleep-related questionnaires, an imaging test, or a formal sleep study.

A Word From Verywell

Falling asleep within five to 15 minutes seems ideal. But if you are out as soon as your head hits the pillow, you may need to take another look at how well and how much you are sleeping. If you fall asleep too quickly, it may be time to visit a sleep specialist to get a better night of rest.