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

If you find that you can nod off quickly, sleep deeply, nap at any time, and fall asleep anywhere, you may consider yourself to be the perfect sleeper. But, while this may seem odd, being able to fall asleep fast can actually be a symptom of a sleeping disorder

How Fast Is Too Fast to Fall Asleep?
Verywell / Brianna Gilmartin

How Does Sleepiness Occur?

First, it's important to understand how we become sleepy. The feeling of sleepiness is due to the accumulation of a chemical within the brain called adenosine. Through the process of energy use and metabolism that occurs with wakefulness, adenosine levels gradually increase. Therefore, sleepiness increases the longer we stay awake.

The process of sleep clears this chemical from our brain through the lymphatic system. As a result, when we wake up in the morning, the levels of adenosine—and sleepiness—are at their lowest and we feel refreshed. 

During the hours you are awake, adenosine levels continue to rise, creating a phenomenon called homeostatic sleep drive. This is sometimes referred to as sleep load or sleep debt.

For example, if you are awake for 30 straight hours, at the end of that time you will be extremely sleepy, fall asleep easily, sleep deeply, and may even sleep longer than you normally would. Here, the levels of adenosine get quite high and compel you towards sleep.

Similarly, if you stay up late at night, past your normal bedtime, you will fall asleep faster because the adenosine levels have increased. But, what happens when these levels are consistently⁠—and sometimes inexplicably⁠—too high?

How Fast Is Too Fast to Fall Asleep?

The time it takes to fall asleep may be a little difficult to judge by the person falling asleep. This is due to a couple of factors.

Firstly, your memory may not fully keep track of the time that you spend dozing off. As a result, you may feel that you are falling asleep faster than you actually are because you don't remember the minutes of wakefulness that were not registered in your long-term memory.

Secondly, the lightest stage of sleep, called stage 1, is one that can be misinterpreted as wakefulness by people who are suddenly awakened from it. Therefore, you may feel as if you were awake longer than you were even though you slipped into (and then maybe out of) light sleep.

The onset of sleep occurs with the loss of muscle tone and a slowing of the electrical waves in the brain, called theta activity. Theta waves, by definition, occur at a speed of four to eight times per second (hertz). By comparison, an alert brain will have electrical waves traveling at twice this rate. So, someone in the lightest stage of sleep will be unconscious and unresponsive to external stimuli from the environment.

The time it takes to transition from wakefulness to sleep is called the sleep onset latency. The only way to objectively measure this is with a measurement of the electrical activity of the brain. This is performed by an electroencephalogram (EEG) as part of a sleep study, called a polysomnogram. Electrodes are placed on the scalp can measure brain waves and tracks 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, this may be a sign of insomnia.

However, if sleep onset occurs in less than five minutes, this may be an indication of a pathological level of sleepiness. It could be a sign of inadequate sleep or fragmented sleep.

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

What Causes Excessive Sleepiness?

The most common cause of sleepiness is sleep deprivation. If you don't get sufficient hours of sleep to feel rested and clear away the adenosine that has accumulated, you will fall asleep faster.

The average person needs just over eight hours of sleep, but there are some people whose sleep needs are more or even less. If you fall asleep quickly, take naps, doze unintentionally, or sleep in on the weekends, these could be indications that you are sleep deprived. Extending your time in bed may be all it takes to ease your sleep debt and allow you to fall asleep a little more slowly.

If sleep is of poor quality and you awaken repetitively throughout the night, this can also contribute to falling asleep too quickly. Referred to as sleep fragmentation, the most common cause is the disorder known as sleep apnea.

In people with sleep apnea, breathing becomes disturbed and leads to frequent arousals during the night. 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.

There are other disorders that can fragment sleep as well. One possibility is restless legs syndrome characterized by periodic movements of the legs at night. Narcolepsy is another in which abrupt transitions of consciousness and unconsciousness occur. When testing does not reveal the cause of excessive sleepiness, it may be diagnosed as idiopathic hypersomnia.

Testing for Excessive Sleepiness

The simplest way to assess sleepiness is by completing a questionnaire called the Epworth sleepiness scale. Higher scores, especially above 10, are correlated with increased sleepiness. Further testing may include a formal sleep study as mentioned above.

Another study called the multiple sleep latency test (MSLT) is also sometimes used to assess excessive sleepiness and the possibility of narcolepsy. The MSLT consists of opportunities to take naps for 20 minutes every two hours during a day. 

On the MSLT, it is considered abnormal if the subject falls asleep on average in less than eight minutes and if there is the onset of rapid eye movement (REM) sleep in two or more of the nap opportunities. This latter finding is highly indicative of narcolepsy.

Imaging Studies

In recent years, sleep experts have begun to endorse the use of imaging tests, like positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), to investigate severe sleep disorders that are resistant to treatment.

Though expensive, these tools are able to track blood flow in the brain indicative of homeostatic sleep pressure (the abnormal desire to want to fall asleep). These changes can directly impact the circadian rhythm and may help characterize the nature and/or cause of sleep deprivation.

In some cases, imaging studies may reveal that the cause of sleep fragmentation is not a sleep disorder per se but rather a symptom of an underlying neurological disorder. One such example is early-stage Parkinson's disease for which sleep fragmentation is a common feature.

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.

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Article Sources

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