Could Falling Asleep Too Fast Be a Sign of a Sleep Problem?

Excessive Sleepiness May Occur in Sleep Deprivation, Sleep Apnea and Narcolepsy

Man Asleep in Bed
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You may consider yourself a perfect sleeper if you fall asleep quickly, you sleep extremely deeply, and it seems that you could take a nap at any time and fall asleep anywhere. It may seem odd, but being able to fall asleep fast can actually be a symptom of a sleeping disorder.

How Does Sleepiness Occur?

First, it is 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. As a result, when we wake up in the morning the levels of adenosine, and sleepiness, are the lowest and we feel refreshed. 

As you are awake, your adenosine levels continue to rise, creating a phenomenon called homeostatic sleep drive. This is also sometimes referred to as sleep load or sleep debt. For example, if you are kept awake for 30 straight hours, at the end of that time you will be extremely sleepy, fall asleep easily, sleep deeply, and you may even sleep longer than you normally would. The levels of adenosine would get quite high and compel you towards sleep. 

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. One of the complicating features is that memory may not fully retain some of the time that you spend dozing off. As a result, you may feel like you fall asleep faster than you actually do because you don't remember the minutes of wakefulness that were not registered in your long-term memory before they were lost forever.

Tipping the balance in the other direction, the lightest stage of sleep, called stage 1, is the first state entered and is misinterpreted as wakefulness by more than half of the people who are awakened from it. Therefore, you might conversely feel like you were awake longer at the start of the night even though you slipped into light sleep.

The only way to objectively verify the time it takes to fall asleep is with the measurement of the electrical activity of the brain with an electroencephalogram (EEG) as part of a sleep study, called a polysomnogram. Electrodes are placed on the scalp to measure brain waves.

Sleep onset occurs with the loss of muscle tone and a slowing of these electrical waves, 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. Someone in this lightest stage of sleep will be unconscious and unresponsive to external stimuli. The time it takes to transition from wakefulness to sleep is called the sleep onset latency.

In general, the average person without excessive sleepiness should fall asleep in five to 15 minutes. If it takes longer than 20 minutes to fall asleep, this may be a sign of insomnia. If sleep onset occurs in less than 5 minutes, this may be an indication of a pathological level of sleepiness. It may be an indication of inadequate sleep or that a sleep disorder may be undermining sleep quality.

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, to clear away the adenosine that has accumulated, you will fall asleep faster. The average person needs just over 8 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.

If sleep is of poor quality, this can also contribute to falling asleep too quickly. The most common cause of sleep fragmentation is sleep apnea. In this condition, which is often associated with loud snoring, breathing becomes disturbed and leads to frequent arousals and awakenings during the night. It is associated with other symptoms, including teeth grinding and going to the bathroom at night. Fortunately, effective treatments exist that can restore sleep quality.

There are additional sleep disorders that may fragment sleep at night. One possibility is movements of the legs at night, which may be associated with restless legs syndrome. Fragmented sleep may also correlate with fragmented wakefulness in narcolepsy, a disorder in which abrupt transitions of consciousness can occur. When testing does not reveal the cause of the excessive sleepiness, it is sometimes labeled idiopathic hypersomnia.

Testing for Sleepiness

The simplest way to assess sleepiness is by completing a questionnaire called the Epworth sleepiness scale. Higher scores, especially above 8, are correlated with increased sleepiness. Further testing may include a formal sleep study as described 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 2 hours during a day. On the MSLT, it is considered abnormal if the subject falls asleep on average in less than 8 minutes and if there is the onset of rapid eye movement (REM) sleep in 2 or more of the nap opportunities, a finding that is highly indicative of narcolepsy.

In summary, 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 with a sleep specialist.

Source:

Kryger, MH et al. "Principles and Practice of Sleep Medicine." Elsevier, 5th edition.

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