Table of ContentsView AllTable of ContentsHow Sleepiness OccursHow Fast Is Too Fast?Causes of Excessive SleepinessTesting for Excessive SleepinessWhen to Talk to Your Healthcare ProviderFrequently Asked Questions
Table of ContentsView All
View All
Table of Contents
How Sleepiness Occurs
How Fast Is Too Fast?
Causes of Excessive Sleepiness
Testing for Excessive Sleepiness
When to Talk to Your Healthcare Provider
Frequently Asked Questions
Some people can nod off quickly, sleep deeply, or nap anytime and anywhere. But being able to fall asleep so fast can actually be a symptom of asleep disorder.
Healthy people normally take about 10 to 20 minutes to fall asleep, with this time referred to as asleep latencyperiod.Dropping off right away might be because you’re so tired but it also may be a sign of an underlying health issue like sleep apnea, or a thyroid issue (known to cause sleep latency changes).
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. The typical process involves the following:
If you were awake for 30 straight hours, you would feelextremely sleepy. But even staying up past your normal bedtime can mean you fall asleep faster because your adenosine levels are up.
How Long Should It Take To Fall Asleep?
In healthy people, sleep latency (the time until you fall asleep) is about 10 to 20 minutes. If it takes longer than 20 to 30 minutes, it could be a sign ofinsomnia. But falling asleep in less than five minutes could signal an unhealthy level of sleepiness, too.
You’re considered “asleep” when your muscle tone relaxes and the electrical waves in your brain slow down. These brain waves are calledtheta 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.
It May Take Longer Than You ThinkYou may not know how long it takes to fall asleep. Yourlong-term memorymay not keep track of the time you spend dozing off. Further, the lighteststage of sleepcan be misinterpreted as wakefulness if you are suddenly awakened from it.You may feel as if you were awake longer but really slipped in and out of light sleep.
It May Take Longer Than You Think
You may not know how long it takes to fall asleep. Yourlong-term memorymay not keep track of the time you spend dozing off. Further, the lighteststage of sleepcan be misinterpreted as wakefulness if you are suddenly awakened from it.You may feel as if you were awake longer but really slipped in and out of light sleep.
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Reasons for Falling Asleep Fast
There are a number of reasons for why you fall asleep fast, including the possibility that a short sleep latency period is normal for you. In most cases, though, there is a contributing factor or condition.
Sleep Deprivation
The most common cause of sleepiness issleep deprivation. If you don’t get enough hours of sleep to feel rested and to clear away the adenosine, you will fall asleep faster. Most people need about seven or more hours of sleep.Some people mayneed 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.
Sleep Fragmentation
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.A common cause issleep 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, effectivetreatmentsexist to restore sleep quality.
Other Sleep Disorders
Other disorders can fragment sleep as well. One possibility isrestless legs syndrome. It causes an uncomfortable feeling that you need to move your legs.Narcolepsyis another possibility. This sleep disorder causes you to slip into sleep without warning during waking hours.
Other causes of sleep fragmentation can include:
When sleep specialists can’t pinpoint exactly why you’re so sleepy, it may be diagnosed asidiopathic hypersomnia. That’s the medical term for excessive sleepiness with no known cause.
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Thyroid Disorders
Some studies have shown that people withhypothyroidism(low thyroid levels) have longer sleep latency periods, even when their thyroid symptoms are below levels considered clinical.The research on the connection has led to mixed results, however, with no clear understanding of the link between thyroid function and sleep.
The connection may be more established in people withhyperthyroidism(excessive thyroid function) who have trouble falling asleep. More than one study has shown a relationship, including one that showed a direct correlation between insomnia andthyroid hormonelevels.
Hyperthyroidism also may contribute to other conditions that disrupt sleep, such as anxiety.People with hypothyroidism may be more at risk for sleep apnea and related disruptions.
Maybe It’s Just Normal for YouSleep efficiencyis the amount of time you’re actually asleep while in bed. A sleep efficiency of 85% or higher is considered normal, and 90% or better is very good.Part of good sleep efficiency is the ability to fall asleep within a normal sleep latency window. For some people, it’s just a part of their makeup, while others may need help. Check with a healthcare provider if you have concerns.
Maybe It’s Just Normal for You
Sleep efficiencyis the amount of time you’re actually asleep while in bed. A sleep efficiency of 85% or higher is considered normal, and 90% or better is very good.Part of good sleep efficiency is the ability to fall asleep within a normal sleep latency window. For some people, it’s just a part of their makeup, while others may need help. Check with a healthcare provider if you have concerns.
Can Your Thyroid Gland and Thyroid Hormones Cause Sleep Disorders?
Testing
Themultiple sleep latency test (MSLT)can also be used to measure sleepiness. It is sometimes used to check for narcolepsy, and often follows a formal sleep study. With an MSLT, you are given a chance to take 20-minute naps in a sleep clinic, every two hours during a day.
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.
However, studies show a wide variation of results with an MSLT test; children, for example, don’t appear to follow the same patterns as adults.
If you find it too easy or too hard to fall asleep, or if you have trouble staying asleep, you may have a sleep disorder. Symptoms of daytime fatigue, with cognitive challenges like forgetting things or simply dozing off too easily, may be clues to problems with yoursleep architecture.
They also may point to an underlying health condition, like a thyroid disorder that requires diagnosis and treatment. Your provider can assess the cause of your sleep latency challenges, sometimes with tests that include a formal sleep study, and then discuss further options with you.
In some cases, lifestyle changes (like establishing a bedtime routine or avoiding late-night screen time) may be a part of improving your overallsleep hygiene. You also may want to discuss using a wearable device, like a watch, or apad trackerplaced under the mattress to monitor your sleep.
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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.
Learn MoreTips for Getting a Good Night’s Sleep
Some people sleep 10 or more hours at a time. “Long sleepers” may be at risk for obesity, diabetes, high blood pressure, and depression. Researchers have also found that they have a 20% to 30% higher risk of early death than normal sleepers.Those risks may be because long sleepers tend to be older adults or those with poor health.Learn MoreHow Much Sleep Do You Need?
Some people sleep 10 or more hours at a time. “Long sleepers” may be at risk for obesity, diabetes, high blood pressure, and depression. Researchers have also found that they have a 20% to 30% higher risk of early death than normal sleepers.Those risks may be because long sleepers tend to be older adults or those with poor health.
Learn MoreHow Much Sleep Do You Need?
15 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Sleep Foundation.Sleep latency.Arosemena MA, Ramos AR, Marcus EN, Slota KA, Cheung J, Castillo PR.Primary hypothyroidism and chronotypes in adult women.BMC Res Notes. 2022 Feb 14;15(1):52. doi:10.1186/s13104-022-05934-3.Fang Z, Rao H.Imaging homeostatic sleep pressure and circadian rhythm in the human brain.J Thorac Dis. 2017;9(5):E495-8. doi:10.21037/jtd.2017.03.168Zhang H, Jacobs J.Traveling theta waves in the human hippocampus.J Neurosci. 2015;35(36):12477-87. doi:10.1523/JNEUROSCI.5102-14.2015Rattenborg NC, De la Iglesia HO, Kempenaers B, Lesku JA, Meerlo P, Scriba MF.Sleep research goes wild: new methods and approaches to investigate the ecology, evolution and functions of sleep.Philos Trans R Soc Lond B Biol Sci. 2017;372(1734):20160251. doi:10.1098/rstb.2016.0251Sleep Foundation.How much sleep do you need?Bhagavan SM, Sahota PK.Sleep Fragmentation and Atherosclerosis: is There a Relationship?Mo Med. 2021 May-Jun;118(3):272-276. PMID: 34149089Song L, Lei J, Jiang K, Lei Y, Tang Y, Zhu J,et al.The Association Between Subclinical Hypothyroidism and Sleep Quality: A Population-Based Study.Risk Manag Healthc Policy. 2019 Dec 19;12:369-374. doi:10.2147/RMHP.S234552.Green ME, Bernet V, Cheung J.Thyroid Dysfunction and Sleep Disorders.Front Endocrinol (Lausanne). 2021 Aug 24;12:725829. doi:10.3389/fendo.2021.725829.Lencu C, Alexescu T, Petrulea M, Lencu M.Respiratory manifestations in endocrine diseases.Clujul Med. 2016;89(4):459-463. doi:10.15386/cjmed-671Reed DL, Sacco WP.Measuring sleep efficiency: What should the denominator be?.J Clin Sleep Med. 2016;12(2):263–266. doi:10.5664/jcsm.5498Ruoff C, Rye D.The ICSD-3 and DSM-5 guidelines for diagnosing narcolepsy: clinical relevance and practicality.Curr Med Res Opin. 2016 Oct;32(10):1611-1622. doi:10.1080/03007995.2016.1208643.Cairns A, Trotti LM, Bogan R.Demographic and nap-related variance of the MSLT: results from 2,498 suspected hypersomnia patients: Clinical MSLT variance.Sleep Med. 2019 Mar;55:115-123. doi: 10.1016/j.sleep.2018.12.013.Markwald RR, Iftikhar I, Youngstedt SD.Behavioral strategies, including exercise, for addressing insomnia.ACSM’S Health & Fitness Journal. 2018;22(2):23-29. doi:10.1249%2FFIT.0000000000000375Léger D, Beck F, Richard J-B, Sauvet F, Faraut B.The risks of sleeping “too much”. Survey of a national representative sample of 24671 adults.PLoS ONE. 2014;9(9):e106950. doi:10.1371%2Fjournal.pone.0106950
15 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Sleep Foundation.Sleep latency.Arosemena MA, Ramos AR, Marcus EN, Slota KA, Cheung J, Castillo PR.Primary hypothyroidism and chronotypes in adult women.BMC Res Notes. 2022 Feb 14;15(1):52. doi:10.1186/s13104-022-05934-3.Fang Z, Rao H.Imaging homeostatic sleep pressure and circadian rhythm in the human brain.J Thorac Dis. 2017;9(5):E495-8. doi:10.21037/jtd.2017.03.168Zhang H, Jacobs J.Traveling theta waves in the human hippocampus.J Neurosci. 2015;35(36):12477-87. doi:10.1523/JNEUROSCI.5102-14.2015Rattenborg NC, De la Iglesia HO, Kempenaers B, Lesku JA, Meerlo P, Scriba MF.Sleep research goes wild: new methods and approaches to investigate the ecology, evolution and functions of sleep.Philos Trans R Soc Lond B Biol Sci. 2017;372(1734):20160251. doi:10.1098/rstb.2016.0251Sleep Foundation.How much sleep do you need?Bhagavan SM, Sahota PK.Sleep Fragmentation and Atherosclerosis: is There a Relationship?Mo Med. 2021 May-Jun;118(3):272-276. PMID: 34149089Song L, Lei J, Jiang K, Lei Y, Tang Y, Zhu J,et al.The Association Between Subclinical Hypothyroidism and Sleep Quality: A Population-Based Study.Risk Manag Healthc Policy. 2019 Dec 19;12:369-374. doi:10.2147/RMHP.S234552.Green ME, Bernet V, Cheung J.Thyroid Dysfunction and Sleep Disorders.Front Endocrinol (Lausanne). 2021 Aug 24;12:725829. doi:10.3389/fendo.2021.725829.Lencu C, Alexescu T, Petrulea M, Lencu M.Respiratory manifestations in endocrine diseases.Clujul Med. 2016;89(4):459-463. doi:10.15386/cjmed-671Reed DL, Sacco WP.Measuring sleep efficiency: What should the denominator be?.J Clin Sleep Med. 2016;12(2):263–266. doi:10.5664/jcsm.5498Ruoff C, Rye D.The ICSD-3 and DSM-5 guidelines for diagnosing narcolepsy: clinical relevance and practicality.Curr Med Res Opin. 2016 Oct;32(10):1611-1622. doi:10.1080/03007995.2016.1208643.Cairns A, Trotti LM, Bogan R.Demographic and nap-related variance of the MSLT: results from 2,498 suspected hypersomnia patients: Clinical MSLT variance.Sleep Med. 2019 Mar;55:115-123. doi: 10.1016/j.sleep.2018.12.013.Markwald RR, Iftikhar I, Youngstedt SD.Behavioral strategies, including exercise, for addressing insomnia.ACSM’S Health & Fitness Journal. 2018;22(2):23-29. doi:10.1249%2FFIT.0000000000000375Léger D, Beck F, Richard J-B, Sauvet F, Faraut B.The risks of sleeping “too much”. Survey of a national representative sample of 24671 adults.PLoS ONE. 2014;9(9):e106950. doi:10.1371%2Fjournal.pone.0106950
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Sleep Foundation.Sleep latency.Arosemena MA, Ramos AR, Marcus EN, Slota KA, Cheung J, Castillo PR.Primary hypothyroidism and chronotypes in adult women.BMC Res Notes. 2022 Feb 14;15(1):52. doi:10.1186/s13104-022-05934-3.Fang Z, Rao H.Imaging homeostatic sleep pressure and circadian rhythm in the human brain.J Thorac Dis. 2017;9(5):E495-8. doi:10.21037/jtd.2017.03.168Zhang H, Jacobs J.Traveling theta waves in the human hippocampus.J Neurosci. 2015;35(36):12477-87. doi:10.1523/JNEUROSCI.5102-14.2015Rattenborg NC, De la Iglesia HO, Kempenaers B, Lesku JA, Meerlo P, Scriba MF.Sleep research goes wild: new methods and approaches to investigate the ecology, evolution and functions of sleep.Philos Trans R Soc Lond B Biol Sci. 2017;372(1734):20160251. doi:10.1098/rstb.2016.0251Sleep Foundation.How much sleep do you need?Bhagavan SM, Sahota PK.Sleep Fragmentation and Atherosclerosis: is There a Relationship?Mo Med. 2021 May-Jun;118(3):272-276. PMID: 34149089Song L, Lei J, Jiang K, Lei Y, Tang Y, Zhu J,et al.The Association Between Subclinical Hypothyroidism and Sleep Quality: A Population-Based Study.Risk Manag Healthc Policy. 2019 Dec 19;12:369-374. doi:10.2147/RMHP.S234552.Green ME, Bernet V, Cheung J.Thyroid Dysfunction and Sleep Disorders.Front Endocrinol (Lausanne). 2021 Aug 24;12:725829. doi:10.3389/fendo.2021.725829.Lencu C, Alexescu T, Petrulea M, Lencu M.Respiratory manifestations in endocrine diseases.Clujul Med. 2016;89(4):459-463. doi:10.15386/cjmed-671Reed DL, Sacco WP.Measuring sleep efficiency: What should the denominator be?.J Clin Sleep Med. 2016;12(2):263–266. doi:10.5664/jcsm.5498Ruoff C, Rye D.The ICSD-3 and DSM-5 guidelines for diagnosing narcolepsy: clinical relevance and practicality.Curr Med Res Opin. 2016 Oct;32(10):1611-1622. doi:10.1080/03007995.2016.1208643.Cairns A, Trotti LM, Bogan R.Demographic and nap-related variance of the MSLT: results from 2,498 suspected hypersomnia patients: Clinical MSLT variance.Sleep Med. 2019 Mar;55:115-123. doi: 10.1016/j.sleep.2018.12.013.Markwald RR, Iftikhar I, Youngstedt SD.Behavioral strategies, including exercise, for addressing insomnia.ACSM’S Health & Fitness Journal. 2018;22(2):23-29. doi:10.1249%2FFIT.0000000000000375Léger D, Beck F, Richard J-B, Sauvet F, Faraut B.The risks of sleeping “too much”. Survey of a national representative sample of 24671 adults.PLoS ONE. 2014;9(9):e106950. doi:10.1371%2Fjournal.pone.0106950
Sleep Foundation.Sleep latency.
Arosemena MA, Ramos AR, Marcus EN, Slota KA, Cheung J, Castillo PR.Primary hypothyroidism and chronotypes in adult women.BMC Res Notes. 2022 Feb 14;15(1):52. doi:10.1186/s13104-022-05934-3.
Fang Z, Rao H.Imaging homeostatic sleep pressure and circadian rhythm in the human brain.J Thorac Dis. 2017;9(5):E495-8. doi:10.21037/jtd.2017.03.168
Zhang H, Jacobs J.Traveling theta waves in the human hippocampus.J Neurosci. 2015;35(36):12477-87. doi:10.1523/JNEUROSCI.5102-14.2015
Rattenborg NC, De la Iglesia HO, Kempenaers B, Lesku JA, Meerlo P, Scriba MF.Sleep research goes wild: new methods and approaches to investigate the ecology, evolution and functions of sleep.Philos Trans R Soc Lond B Biol Sci. 2017;372(1734):20160251. doi:10.1098/rstb.2016.0251
Sleep Foundation.How much sleep do you need?
Bhagavan SM, Sahota PK.Sleep Fragmentation and Atherosclerosis: is There a Relationship?Mo Med. 2021 May-Jun;118(3):272-276. PMID: 34149089
Song L, Lei J, Jiang K, Lei Y, Tang Y, Zhu J,et al.The Association Between Subclinical Hypothyroidism and Sleep Quality: A Population-Based Study.Risk Manag Healthc Policy. 2019 Dec 19;12:369-374. doi:10.2147/RMHP.S234552.
Green ME, Bernet V, Cheung J.Thyroid Dysfunction and Sleep Disorders.Front Endocrinol (Lausanne). 2021 Aug 24;12:725829. doi:10.3389/fendo.2021.725829.
Lencu C, Alexescu T, Petrulea M, Lencu M.Respiratory manifestations in endocrine diseases.Clujul Med. 2016;89(4):459-463. doi:10.15386/cjmed-671
Reed DL, Sacco WP.Measuring sleep efficiency: What should the denominator be?.J Clin Sleep Med. 2016;12(2):263–266. doi:10.5664/jcsm.5498
Ruoff C, Rye D.The ICSD-3 and DSM-5 guidelines for diagnosing narcolepsy: clinical relevance and practicality.Curr Med Res Opin. 2016 Oct;32(10):1611-1622. doi:10.1080/03007995.2016.1208643.
Cairns A, Trotti LM, Bogan R.Demographic and nap-related variance of the MSLT: results from 2,498 suspected hypersomnia patients: Clinical MSLT variance.Sleep Med. 2019 Mar;55:115-123. doi: 10.1016/j.sleep.2018.12.013.
Markwald RR, Iftikhar I, Youngstedt SD.Behavioral strategies, including exercise, for addressing insomnia.ACSM’S Health & Fitness Journal. 2018;22(2):23-29. doi:10.1249%2FFIT.0000000000000375
Léger D, Beck F, Richard J-B, Sauvet F, Faraut B.The risks of sleeping “too much”. Survey of a national representative sample of 24671 adults.PLoS ONE. 2014;9(9):e106950. doi:10.1371%2Fjournal.pone.0106950
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