What causes sleep inertia?

What causes sleep inertia?

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Sometimes after a nap, I wake up in a state of grogginess. I learned that this is actually called sleep inertia. I'm able to find lots of methods to overcome this, but what causes it in the first place?

This is due to states of brain activation promoted by the reticular formation, specifically with the ascending reticular activating system that mediates the general activation of the upper areas, for sleep these areas should promote states of relative low activity promoting the cerebral activation profiles during sleep, it is also interesting to study the descending reticular activating system that mediates the general muscular activation that is generally inhibited during sleep (except clinical problems among others) (that is why you can not make muscular efforts when waking up, try an experiment: try to clench your fists strongly when you are awakening).

Brain Basics: Understanding Sleep

Sleep is an important part of your daily routine&mdashyou spend about one-third of your time doing it. Quality sleep &ndash and getting enough of it at the right times -- is as essential to survival as food and water. Without sleep you can&rsquot form or maintain the pathways in your brain that let you learn and create new memories, and it&rsquos harder to concentrate and respond quickly.

Sleep is important to a number of brain functions, including how nerve cells (neurons) communicate with each other. In fact, your brain and body stay remarkably active while you sleep. Recent findings suggest that sleep plays a housekeeping role that removes toxins in your brain that build up while you are awake.

Everyone needs sleep, but its biological purpose remains a mystery. Sleep affects almost every type of tissue and system in the body &ndash from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Research shows that a chronic lack of sleep, or getting poor quality sleep, increases the risk of disorders including high blood pressure, cardiovascular disease, diabetes, depression, and obesity.

Sleep is a complex and dynamic process that affects how you function in ways scientists are now beginning to understand. This booklet describes how your need for sleep is regulated and what happens in the brain during sleep.

Science Says This Is Exactly How To Nap To Be At Your Best

Is it good to take naps during the day? originally appeared on Quora: the knowledge sharing network where compelling questions are answered by people with unique insights.

It's great to take naps during the day, but only if you do it correctly. It is much better to take naps than to stay awake for extended periods of time attempting to finish all your tasks, because, let's face it, 8-9 hours of sleep a day is not always possible. Naps "reboot" your brain and help you approach your work with a fresh and clear state of mind.

You can choose the length of your nap in order to cater to your specific need. Yes, how long you should nap is based on your reason for napping.

The power nap is 10 to 20 minutes long. Take a power nap to quickly boost your energy and alertness. A power nap will help you get back to work right away. This is because this amount of sleep does not yet reach the deeper states of a sleep cycle and it should be easy to get up and work again. The napper stays in the lighter stages of NREM (non-rapid eye movement) sleep.

Avoid 30-minute naps. There are no significant benefits to this length of nap. Half-hour naps cause "sleep inertia," a groggy state than can last for about 30 minutes after waking up. This is because the body is forced awake right after beginning, but not completing, the deeper stages of sleep. Sleeping for 60 minutes includes the deepest type of sleep, slow-wave sleep. Because of this, the one-hour nap is ideal for helping an individual better remember faces, names, and facts. However, a sleep cycle will not be completed in only 60 minutes, so you may not be very alert for some time after waking up.

The most ideal nap is the 90-minute nap. Why? 90 minutes is the length of one full sleep cycle, which includes all the light and deep (REM and dreaming) stages of sleep. A full sleep cycle nap improves procedural and emotional memory (e.g. for playing musical instruments and driving). A 90-minute nap can also significantly boost one's creativity. Because the nap is a full sleep cycle, waking up should come much easier.

There are optimal times for napping throughout the day that depend on the time you wake up in the morning. If at all possible, try to plan your naps during these times.

According to sleep researcher Dr. Sara Mednick, the optimal napping time is the time of day where slow-wave sleep (deep sleep) and REM intersect. Use her interactive nap wheel to determine what time you should nap based on when you woke up. Below is an example nap wheel for a person that woke up 7 am. This person should nap at 2 pm (or 2 am if not yet asleep).

This question originally appeared on Quora. Ask a question, get a great answer. Learn from experts and access insider knowledge. You can follow Quora on Twitter, Facebook, and Google+. More questions:

How can you improve your sleep patterns?

We already know that physical and mental health conditions—be in chronic pain, sleep apnea or depression and anxiety—impact sleep patterns, which in turn affects the body’s immune system adversely. Now more than ever, in this COVID-19 era, we need to pay more attention to our sleep.

Some preventive and restorative measures recommended by Brahmbhatt include setting a sleep-wake schedule (and staying away from gadgets an hour before sleeping and an hour after waking up), getting some natural sunshine earlier in the day which helps produce serotonin (the happy hormone) in the day and melatonin (the sleep-inducing hormone ) at night, sitting up in bed and meditating for the first 10-15 minutes, doing a few simple exercises and stretches even if for 5-10 minutes to increase blood circulation and replacing caffeine (the well-known sleep disruptor) in the morning with either infused or plain water to combat dehydration and kickstart internal organs.

“Diet also plays a very important role. Early and light meals help one to wake up feeling refreshed. Extreme late nights combined with heavy food and alcohol can also result in sleep inertia,” says Brahmbhatt. She suggests a few home remedies for the same, but adds, “If sleep inertia is debilitating to the point that it affects one’s life and ruins the first half of the day completely, then professional help is needed.” One option is mudra therapy, where specific mudras or hand postures are used to allow the body’s energy channels to flow freely, eliminates blockages. As a result, balance is restored and one feels mentally and physically healthy. She also suggests pranayama, a breathing technique that is known to resolve many psychosomatic illnesses, resulting in restful sleep. “Ultimately, irrespective of one being an early bird or a night owl, restful sleep should result in feeling refreshed and recharged, with a spring in your step,” says Brahmbhatt.

Avoiding and Treating Sleep Inertia

There are two strategies to cope with sleep inertia: avoiding it or treating it. In an ideal world, you would try to avoid sleep inertia altogether and only treat it when extenuating circumstances require you to do so.

How to Avoid Sleep Inertia

In order to avoid sleep inertia, the best thing to do is to go to bed and wake up at roughly the same time every day. This allows your circadian rhythm, which is your internal biological clock, to function on a regular schedule. If your wakeup time is somewhat flexible, allow your mind to wake you up naturally, rather than relying on an alarm.

If you must wake up by a certain time, try using an alarm clock that uses light rather than sound to wake you up. These alarm clocks will begin to simulate daylight half an hour before your wake-up time, gradually brightening the room over the next thirty minutes.

Researchers have found that light exposure can impact hormone release, including melatonin, the sleep hormone, leading to reduced stress and enhanced feelings of well-being and alertness.

How to Treat Sleep Inertia

When you roll out of bed and realize that your prefrontal cortex is still slumbering the day away, there are countermeasures that you have to combat it:

  1. Caffeine: Coffee and tea are idolized around the world for their impact on our emotions and cognitive function. Consuming these caffeinated beverages combats fatigue, improves reaction time, and offers certain cognitive enhancements. Grab a cup of coffee or black tea when you’re feeling particularly tired.
  2. Temperature: Have you ever gone outside early in the morning on a particularly chilly day and woken right up? Cold temperature exposure can quickly boost mental alertness and fight general fatigue. Give a cold shower a try to wake yourself up quickly at any time of year.
  3. Daylight exposure: Our bodies respond to the natural light/dark cycle, and research suggests that light exposure can help to suppress our sleep hormone melatonin while enhancing cognition and mental alertness. Try exposing yourself to daylight or bright indoor lights to help boost alertness.
  4. Take a short nap: A nap shorter than 30 minutes may help to lessen sleep inertia, which can be particularly useful for those who perform on-call duties or night-shift work.

Sleep Inertia

Ever felt foggy, drowsy or disorientated after you’ve woken up? You’re suffering from sleep inertia – the feeling of grogginess after waking up, because you’re still in a sleep state.

It usually lasts from around five to 30 minutes but it can last for as long as two to four hours. During this time you may feel like your concentration is impaired and you don’t feel as alert.

What causes sleep inertia?

Sleep inertia (or morning grogginess) occurs when you wake suddenly during slow-wave sleep.

The brainstem arousal system is the part of the brain responsible for basic physical functioning. Though it’s activated immediately upon waking, our prefrontal cortex (PFC), which oversees decision-making and self control, takes a while to get going. It can be up to 30 minutes for our PFC to catch up with the rest of our body.


Sleep inertia is often experienced after napping because we wake mid sleep cycle. The best advice for napping is to limit to approx. 20 minutes to prevent waking during deep or slow-wave sleep.

How to avoid sleep inertia

If you’re sleep deprived, sleep inertia is worse and can last longer. Being well-rested is key – that means optimising both sleep quantity and sleep quality. Sticking to regular bed times and wake times will help to programme your mind and body to sleep better which will help regulate your body clock.

Ideally, waking up naturally is the best way to avoid sleep inertia. Being rudely awakened from sleep means our melatonin levels are still high causing sleepiness. Natural light is a great way of suppressing melatonin levels and reducing sleep inertia to make you wake feeling more refreshed.

However as most people need an alarm to wake them for school/work etc try to plan it to go off at the end of a sleep cycle. The best thing is to work backwards from the time you want to get up in a morning to give you an ideal bedtime. Multiply 90 minutes (each cycle time) by five (the number of sleep cycles per night) to get 450 minutes or 7.5 hours of sleep. Allow yourself around 15 minutes to drop off to sleep. Therefore, if you need to wake up by 7am then count back 7.5 hours plus 15 mins (to nod off) to find that lights out time is around 11.15pm. Make sure you’re in bed before then so you’re relaxed ready for sleep.

Also avoid pressing the snooze button. If you press the snooze button, your brain knows it’ll go off again. You won’t get any of the deep, resting slumber in between snoozes. Set your alarm for when you definitely have to get up. If you have a hard time not pressing the snooze button, try putting it across the room so you have to walk over there, waking you up along the way.

Practice good sleep hygiene principles such as winding down before bedtime, avoiding caffeine and alcohol in the evening and creating a sleep friendly bedroom.

At-Home Treatment

Treating mild forms of sleep inertia can be done in the comfort of your own home without professional intervention. Below you’ll find a few reactive countermeasures that may help.


Consuming caffeine is a popular means of combating the effects of sleep inertia in an effort to provide that feeling of wakefulness and energy. Despite its overwhelming popularity, you should still make sure to consume caffeine with care. It can easily disrupt your ability to sleep during your regular sleep time, and therefore shouldn’t be used to tackle sleepiness before bed. Consider utilizing caffeine with other natural substances like L-theanine to ensure it doesn’t overload you with energy.


Most of us love a short nap (if time allows), but it’s important to note that the nap itself must be rather short indeed. A nap to combat drowsiness should be between 10 and 20 minutes, and it should take place in the afternoon. Taking a nap to combat prior sleep deprivation also isn’t a healthy idea, as your body desperately needs hours of sleep rather than a brief sleep episode.

Light Exposure

Light exposure is a healthy and natural means of waking your body and mind if you find yourself suffering from sleep inertia. All it takes is a dose of natural sunlight for your body to suppress melatonin levels (the hormone that regulates your sleep-wake cycles) and get you going should grogginess be an issue. It should be noted, however, that only exposure to natural sunlight will do the trick white light or artificial light isn’t sufficient.

The Subtraction Task

Some individuals utilize what is known as the subtraction task to increase brain activity and reduce the sleep inertia period. Many apps such as Mathe Alarm Clock now offer an alarm clock that can only be turned off after you’ve completed a simple subtraction equation, thus ensuring you’re awake enough to answer the question and get out of bed.

Sleep Schedule Alterations

Consider altering your sleep schedule if you find yourself sleeping at odd hours of the day or night. Your body will naturally follow its own circadian rhythm to try and sleep at night when possible, so don’t fight that sleepy feeling when it arises. Consider utilizing a fitness tracker that also contains a sleep tracker so that you can monitor and adjust your sleep schedule as needed.

Other Remedies

Other simple remedies include splashing water on your face or blasting cold air in an effort to wake up. If you’ve found a healthy countermeasure to get you up, don’t be afraid to use it.

How do I stop sleep inertia?

  • the stage of sleep you are in upon awakening
  • how long you have been sleeping for
  • sleep deprivation
  • sleep efficiency

Sleep efficiency refers to the percentage of time a person sleeps, in relation to the total time spent in bed. A normal and healthy sleep efficiency is considered to be 85% or higher. Thus, your sleep efficiency is reduced when any of your sleep stages is interrupted by sudden awakening. As a result, a good night’s rest will allow your body to restore, hence reducing sleep inertia and increasing sleep efficiency. This means optimising both sleep quality and sleep quantity and can be achieved by sticking to a regular routine that will help regulate your body clock.

Although waking up naturally is the best way to avoid sleep inertia, it is not ideal as many people rely on an alarm for school or work. By being suddenly awakened, your melatonin levels are still high, thus causing drowsiness. To counter this, studies have shown that using natural light (ie. catching a glimpse of the sunrise through your window or even through an artificial dawn light) can help speed up the process of feeling fully alert and fresh upon awakening. It also suppresses melatonin levels, therefore decreasing the impacts of sleep inertia.

If you rely on an alarm, calculate backwards from the time you want to wake up in the morning to get an ideal sleep time. Multiply each cycle time , 90 minutes, by the number of sleep cycles per night, 5, to get 450 minutes (7.5 hours) of sleep and add an additional 15 minutes to doze off. For example, if you need to be awake by 7am, count back 7.5 hours plus 15 minutes – this means you should sleep around 11:15pm to get optimal sleep. Furthermore, rather than pressing the snooze button, try to set your alarm for when you definitely have to wake up. If you have trouble not pressing the snooze button, try placing it across your room so you are forced to wake up.

Research has also shown strategic napping may also help counteract sleep inertia, however the timing of the nap is critical ideally 10-20 minutes in the afternoon is the sweet spot. However, a short nap is only effective if a person is not already sleep deprived.

Additionally, caffeine is something you’ve probably already thought about to eliminate the effects of sleep inertia. It helps people feel alert by increasing the amount of cortisol, a stress hormone, in your body and acts as a central nervous system stimulant. You may also try a stick of caffeinated gum as an alternative for coffee. Research has also shown that caffeinated gum helps reduce the effects of sleep inertia in shift workers after a nap.

Moreover you can practice good sleep hygiene to overcome sleep inertia:

  • Avoid using electronic devices at least 30 minutes before sleeping
  • Establish a regular bedtime routine: try reading a book or listen to some calming music to help you unwind
  • Avoid drinking alcohol before bedtime: contrary to how a glass of wine can make you feel sleepy, research shows that drinking alcohol too close to your sleeping time can disrupt your regular sleep time
  • Avoid drinking coffee or other caffeinated beverages before bedtime
  • Avoid eating a big meal close to bedtime: this can put pressure on your oesophageal sphincter, thus causing heartburn and disrupting your sleep. However, if you’re hungry, a light bedtime snack such as milk, kiwis and tart cherries have sleep promoting properties
  • Keep your bedroom dark and cool
  • Stick to a regular sleep routine

For more information, read our article on how to get a good night’s sleep here.


As discussed in the previous sections, sleep inertia is characterized by impaired performance and reduced alertness immediately after waking. These effects dissipate asymptotically with the most significant effects occurring within 30 mins of waking. Sleep inertia interacts with the homeostatic and circadian processes to influence performance immediately after waking. Evidence suggests that waking after acute or chronic prior sleep loss, during the circadian low, or from deeper stages of sleep can exacerbate sleep inertia. Sleep inertia is of great importance as the associated performance impairment can be equivalent to, or greater than, that observed after up to 40 hrs of sleep deprivation. Sleep inertia effects have been observed on a range of tasks from simple reaction time tests to complex cognitive tasks. While field studies of sleep inertia are lacking, evidence of sleep inertia in real-world scenarios has been demonstrated in several operational incidents, often with catastrophic consequences. While there is evidence that caffeine can help to reduce the impact of sleep inertia, there is a need for further research into reactive countermeasures that can be deployed in operational scenarios.

Sleep inertia: current insights

Sleep inertia, or the grogginess felt upon awakening, is associated with significant cognitive performance decrements that dissipate as time awake increases. This impairment in cognitive performance has been observed in both tightly controlled in-laboratory studies and in real-world scenarios. Further, these decrements in performance are exaggerated by prior sleep loss and the time of day in which a person awakens. This review will examine current insights into the causes of sleep inertia, factors that may positively or negatively influence the degree of sleep inertia, the consequences of sleep inertia both in the laboratory and in real-world settings, and lastly discuss potential countermeasures to lessen the impact of sleep inertia.

Keywords: cognitive performance countermeasures grogginess.

Conflict of interest statement

Dr. McHill reports speaker honorarium or travel reimbursement fees from the Utah Sleep Research Society and the California Precast Concrete Association. The authors report no other conflicts of interest in this work.