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Sure, you might be physically awake by the time you step out of bed in the morning or after an afternoon nap, but if you attempted to solve a math equation or explain a complex topic immediately post-snooze, your brain might say otherwise. That’s because waking up is less like a switch being flicked on, and more like turning up a dimmer—a process that can be explained by the concept of sleep inertia. Much like its physics namesake, sleep inertia means that an object at rest (in this case, you) stays at rest unless acted upon by an outside force (say, an alarm clock). While sleep inertia endures, you may feel drowsy, disoriented, or just not all there. As such, the amount of time it takes for your brain to get into high-functioning work mode upon waking up hinges directly on how long that sleep inertia period lasts.
Experts in This Article
Daniel Barone, MD, is currently the Associate Medical Director of the Weill Cornell Center for Sleep Medicine, an Associate Professor of Clinical Neurology at Weill Cornell Medical College, and an Attending Neurologist at New York-Presbyterian/Weill Cornell Medical Center. He specializes in the evaluation and management of patients with all forms of sleep disorders including sleep apnea, restless legs syndrome, insomnia, and narcolepsy. He is certified by the American Board of Psychiatry and Neurology in both Neurology and Sleep Medicine. He is a member of the American Academy of Neurology, and is a fellow of the American Academy of Sleep Medicine. Dr. Barone’s first book, “Let’s Talk About Sleep,” was published in January, 2018, by Rowman & Littlefield.
“There’s a neurochemical cascade, including a set of hormonal releases, that naturally moves the body between sleep and wakefulness,” says neurologist Daniel Barone, MD, sleep expert at Weill Cornell and New York-Presbyterian, and author of Let’s Talk About Sleep. “It takes time for the body and brain to shift into a fully activated state.”
“There’s a neurochemical cascade, including a set of hormonal releases that naturally moves the body between sleep and wakefulness.” —Daniel Barone, MD
According to a 2019 review of sleep-medicine studies, that sleep-inertia period typically lasts for about 30 minutes (though certain studies have clocked it at as short as 15 minutes), often bringing a dip in both speed and accuracy on cognitive tasks. That said, the review also found that in research measuring both participants’ self-reported levels of alertness and actual performance on cognitive tests, a full brain recovery to pre-sleep levels can take upwards of an hour.
If your sleep-inertia grogginess seems to last any longer than that on a regular basis, Dr. Barone says there might be something else interfering with your sleep-wake cycle. Conditions like chronic insomnia, circadian-rhythm disorders, and sleep apnea could all worsen the effects of sleep inertia, so it’d be wise to consult a medical professional for a plan of action if you suspect any of the above. Beyond those underlying health conditions, however, several other elements can influence how long sleep inertia really lasts—and how long it takes for your brain to fully wake up, as a result.
Factors that can affect the duration of sleep inertia:
Your level of sleep deprivation
While you can certainly develop a baseline level of grogginess from sleep deprivation alone, falling short on sleep for several consecutive nights can also independently increase how long that sleep inertia feeling lasts each morning. That’s because of the way your body tends to restructure sleep when you’re operating in a sleep-deprived state, says Dr. Barone.
The body’s natural response to make up for an acute period of sleep loss (say, a single all-nighter) or longer-term sleep deprivation is to get more efficient, “which means packing in more of that deep delta-wave sleep during the short time you’re asleep, including in the hour or two just before you wake up,” he says. “But in the sleep of someone who’s not sleep-deprived, more of that slow-wave sleep happens in the first part of the night, several hours before they’d be waking up.”
That timing distinction is important because when you wake up directly from a deeper level of sleep (versus experiencing it earlier in the night), your brain has a harder time acclimating to wakefulness. “The brain waves during that deep sleep are these massive undulating waves,” says Dr. Barone, “so it’s a bigger shock to the system to be awakened from that state.”
It’s the same reason experts recommend capping an afternoon nap at 30 minutes. Any longer, and you could move into deep-wave sleep, from which it’ll be all the tougher for your brain to fully wake up.
The time when you’re waking up
Whether you’re waking up from sleep in the early morning, mid-afternoon, or middle of the night can also have an effect on how long the sleep inertia keeps you groggy. The closer you are to your circadian low (aka the low-point in body temperature that happens near the middle of the night) when you wake up, the longer your sleep inertia will last.
In other words, that means you’ll feel groggier for a longer period of time if you try to wake up at 2 or 3 a.m. versus at 8 a.m. or sometime in the middle of the afternoon, regardless of whether you’re sleep-deprived. That’s because the general flow of our circadian rhythm and the related release of hormones supports wakefulness during daytime hours and sleepiness during nighttime ones.
Your sleep chronotype
Not everyone’s circadian rhythm is precisely the same. And the fluctuations that create different chronotypes, or natural sleep-timing preferences (think early birds versus night owls) also affect how long it’ll take to kick sleep inertia and wake your brain up.
Specifically, people with a later chronotype (those who stay up later and wake up later) may take longer to recover from sleep inertia than those with an early chronotype, regardless of when they’re actually waking up. In a small 2017 study of 18 people, researchers found that performance on a visual-attention task among the people with early chronotypes showed significant improvement within 10 to 20 minutes of awakening, whereas performance for the folks with later chronotypes took upwards of 30 minutes to show the same improvement.
How to shift your brain into work mode more quickly
Because your brain will always need some amount of time to push through the effects of sleep inertia after you wake up, simply being aware of that is essential. Once you know that it takes roughly 30 minutes, on average, for the brain to fully awaken and reach its max functionality, you can plan to get up at least that far in advance of having to take a work call or do anything else requiring your full attention.
Making a point of going to bed around the same time each night, clocking seven to eight hours of sleep, and then waking up around the same time each morning can also help align your sleep with your natural circadian rhythm and minimize the sleep-deprivation effects that can worsen or lengthen sleep inertia, says Dr. Barone.
“Getting some sunlight first thing in the morning can also alert the brain that it’s time to wake up by naturally shutting off the production of melatonin,” he says, which can shorten the sleep inertia process, too. And while coffee shouldn’t be the first thing you drink upon waking up, its high dose of caffeine can certainly boost alertness, if you time it right—that is, pouring yourself a cup later in the morning or even trying out the “nappuccino,” which involves drinking a cup right before a power nap, so its effect kicks in just as you’re waking up (aka when you need it most).
—reviewed by Angela Holliday-Bell, MD
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