The Science of Sleep Inertia: Why Waking Up Can Be So Hard

Sleep inertia Can make waking up hard. Learn why sleep inertia occurs and what you can do to prevent it.


Have you ever woken up, whether in the morning or from a nap, and felt worse than you did when you went to sleep? This phenomenon, called sleep inertia, is characterized by disorientation, lagging reaction times, and irritability. In short, it’s unpleasant and can make you wish you’d never fallen asleep.

Sleep inertia often occurs when you awaken while in deep sleep, so the key to avoiding it is changing how and when you wake up. We’ve got some tips you can implement to avoid sleep inertia, along with some quick fixes if it’s too late to prevent it, but you don’t want to let sleep inertia take up any more of your day. 

What is Sleep inertia?

Sleep inertia is the disorientation or worsening mood that you may feel when waking up in the morning or from a nap. It can also cause a decline in performance, such as a slower reaction time and thinking speed, poorer short-term memory, and hindered reasoning and learning. 

Sleep inertia is not a normal part of waking up, but, when it does occur, it generally lasts 30-60 minutes. However, some studies have found that it can last up to 2 hours, and one thing that may make you susceptible to longer bouts of sleep inertia is being sleep-deprived. 

While researchers aren’t entirely sure why sleep inertia occurs, they theorize that it’s due to a protective mechanism your body employs to maintain sleep and avoid waking during the night. However, if you wake before your body is ready, your body may use this mechanism to try and get you back to sleep, causing sleep inertia.

There are multiple theories about what may cause the symptoms of sleep inertia. One is that sleep inertia results from increased delta waves (slow waves), which are most common during the non-rapid eye movement stage of sleep. It’s speculated that sleep inertia may occur if you’re suddenly awoken during NREM sleep before the brain has reduced the delta waves, which it does as it prepares to wake up. Until the delta waves go away, the symptoms of sleep inertia may linger. 

Yet another theory has to do with blood flow to the brain and how it increases or decreases depending on your sleep stage. Sleep inertia may result when you wake up when the blood flow is reduced, leading to symptoms of sleep inertia. 

Finally, sleep inertia may have to do with adenosine, which is a nucleic acid compound in the brain. This compound is crucial for sleep and wakefulness, with adenosine levels being lowest when you wake. However, sleep inertia may occur if your adenosine levels are still high when waking, which can happen if you don’t sleep for long enough.

Avoiding Sleep Inertia

We’ve all likely experienced sleep inertia at some point, and it’s not something you fall asleep hoping to wake up with. It can affect the rest of your day, souring your mood and making it nearly impossible to focus on anything for at least 30 minutes, sometimes longer. And while these symptoms may last for less than an hour, the lingering effects can tinge the rest of your day. 

Instead of assuming that sleep inertia is inevitable and will occur whenever it wants to, try the following tips to prevent it so that you truly feel rested when you wake up.

Keep Naps Short

Naps are a favored way to address fatigue but can also be the most common cause of sleep inertia. It’s not napping itself that is the problem, though; it’s napping for too long. To minimize sleep inertia, keep your naps to 20 minutes or less. It may not seem like much sleep, but it’s the perfect amount of time to rest up without settling into a deeper sleep. 

Try Some Caffeine

If you’re settling down to nap, try drinking a cup of coffee beforehand. Conveniently labeled a “coffee nap,” this strategy of drinking coffee immediately before sleeping allows the effects of caffeine to kick in right when you wake up, so long as you keep the nap to 30 minutes or less. 

The energy-boosting effects of caffeine combine with the restorative effects of a power nap, boosting your energy supply and focus and keeping sleep inertia at bay. 

Get Awoken Gently

You likely use some form of alarm to wake up, but many are loud and jarring, which can contribute to feelings of grogginess or confusion when waking up. Instead, try to modify your wake-ups by using a sunrise alarm clock that gradually increases its brightness and uses gentle sounds to wake you up. 

Yet another alternative is to use an app that can detect when you’re in a light state of sleep and wake you up then, such as Pillow. With Pillow’s help, you can wake when your body is already closest to being awake, minimizing the dreadful feelings of sleep inertia. 

I Have Sleep Inertia, Now What?

If you wake up and are experiencing sleep inertia, you should avoid performing any critical tasks until it dissipates. Anything that requires a quick reaction time (such as driving) or a heavy mental load should be pushed back if you can to avoid making poor decisions or getting into an accident. 

As for how to leave sleep inertia behind faster, research has found that you can use caffeine to your advantage. In one study, the participants saw a reduction in how long sleep inertia lasted by taking 100 mg of caffeine upon awakening. 

Bright light can also help restore alertness more quickly, so if you can, get some sunlight as soon as you wake up to chase away the sleepiness and disorientation. Research has even shown that artificial sunlight using a light box can help. Washing your face, as well, has shown success in helping sleep inertia dissipate.

To review, if you have sleep inertia:

  • Avoid critical tasks
  • Drink caffeine
  • Get some bright light
  • Wash your face

Don’t Feel Sleepy When You’re Awake

Sleep inertia is the disorientation and grogginess you may feel when you wake up. It’s unsettling and can put you in a bad mood while also making it dangerous to perform critical tasks. 

While the cause of sleep inertia isn’t entirely known, research has uncovered ways to prevent sleep inertia from occurring, such as keeping naps short, drinking caffeine, and changing how you’re woken up. In particular, an app such as Pillow can help you wake up in your lightest sleep stage, reducing the likelihood of sleep inertia. 

If you’re currently experiencing sleep inertia, put a hold on important tasks until it dissipates. It usually lasts less than an hour, but try drinking caffeine, getting some bright light, and washing your face to speed it up. 

Sleep inertia can ruin the benefits of sleep, but with the help of Pillow, you can regain your wake-up time. 


Written by

Jessica G

Medical writer freelancer who has written hundreds of articles on varying topics. Masters of Engineering degree in Biomedical Engineering.

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