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What Is Sleep Inertia and How to Beat It?

Guest Author: Caitlin Evans

What is sleep inertia and how do you beat it?

Many of us have long accepted we’re not “morning people” – and if you feel the same, you bet you’re not alone. For at least 15 minutes after waking up, the majority of people simply don’t have it together, mentally speaking. This sluggishness flows into grumpiness, and you just want silence until the fog clears (which, unfortunately, often takes longer than you’d like). Sleep is supposed to be restorative, so why in the world do we feel worse upon waking up than we did when going to bed – even when we get the right amount of sleep? The answer lies in sleep inertia. This phenomenon is researched by sleep scientists and defined as “a physiological state of impaired cognitive and sensory-motor performance that is present immediately after awakening”. It is a transitional period in which some parts of the brain haven’t quite torn themselves away from the sleep state. Here’s what researchers have uncovered about sleep inertia so far.

The stages of sleep

This transitional period of grogginess most people experience upon awakening typically lasts 15 to 60 minutes, but it can last for as long as two hours – or even more. When a person is sleep-deprived, the inertia is even worse because, on top of it all, they’re not rested enough. But studies show that the effects of sleep inertia can be felt even after a “regular” 8-hour period of sleep, and it has a lot to do with the sleep stage we were in prior to awakening.
In order to understand this better, let’s look at a quick overview of the five stages of sleep, the first four of which are classified as non-rapid eye movement (NREM) stages:

  1. The muscles slowly relax and the eyes move as you drift in and out of light sleep. Many people experience muscle twitches or jerking during this stage.
  2. In the second stage, the eye movement stops and brain waves become slower. As you descend into the deeper stages of sleep, the body temperature drops while your breathing and heart rate slow down.
  3. The third stage marks the beginning of deep sleep. The brain starts emitting Delta waves (which are extremely slow brain waves) intermixed with smaller and faster waves.
  4. Deep sleep continues, with the brain emitting almost exclusively Delta waves. Movements are limited; breathing is steady and deep. People feel particularly disoriented when roused from this stage of sleep.
  5. The fifth and last stage marks rapid eye movement (REM) sleep. This stage is important for restoring brain function, as brain waves start mimicking waking-state activity but the body does not move at all.

Now, these stages form a sleep cycle, but they don’t progress straight from the first stage to the fifth – within a sleep cycle, there are periods of reversing from deep sleep to light sleep and going back to deep sleep again. After REM sleep, you return to the first stage and begin a new cycle.

We go through 4-5 sleep cycles on average each night, the first one taking 90 minutes and the rest approximately 100-120 minutes. Furthermore, the amount of time we spend in certain stages of sleep changes over the course of the night, with deep NREM sleep stages dominating in the first few cycles.

What can we take away from all of this?

Quite simply, no matter how much or how wonderfully you’ve slept, if the alarm starts blaring abruptly in the morning and you’re in a stage of deep sleep, sleep inertia is going to hit you hard.

Sleep inertia and the science of waking up

The process of awakening relies on a gradual increase of cerebral blood flow. It takes a while to re-establish normal levels of cerebral blood flow in different regions of the brain, activating them effectively. The more primitive parts of the brain, such as the brainstem and thalamus, are activated instantly upon awakening. With the arousal systems in the brainstem activated instantly, you get a sense of wakefulness and start mobilizing your body.
However, it takes more time to activate the anterior cortical regions. Cerebral blood flow spreads to them after about 15 minutes or so – and there you have it, the minimum amount of time typically attributed

to the transitional period of sleep inertia. This is because the cortical region is responsible for things such as attention, awareness, and perception. Your ability to perform basic cognitive tasks is impacted by this slow reestablishment of cerebral blood flow in the cortical region.

But that’s not all: activating the prefrontal cortex (which is a major part of the cortical region) is crucial to re-establishing your consciousness and personality. This part is most affected by disrupted sleep patterns and it is involved in decision-making as well. All of these factors constitute sleep inertia, and if you, like most of us, have often found yourself struggling to put on clothes or apply toothpaste right after waking up, now you know the science behind it.

How can we avoid sleep inertia?

Now, cerebral blood flow has to be re-established gradually as you wake up, but as you might have gathered from the previous points, there are factors that make sleep inertia significantly worse. That being said, it can be minimized so that the process of fully awakening is, to put it bluntly, much less painful. Here’s how:

  • Get better sleep. Since disrupted sleep patterns have the most negative effect on activating the prefrontal cortex, you want to ensure you get sound sleep that allows proper cycles throughout the night. Watch out for two crucial factors: food and light. Wearing a sleeping mask to help maintain the body’s circadian rhythm is especially important considering the amount of light pollution we’re subjected to even in our sleeping environments. Things are not so straightforward when it comes to food signaling your brain whether it’s time for action, so pay attention to your eating habits in relation to sleep.
  • Get enough sleep. This might sound redundant, but there’s no getting around it. In our busy modern lifestyles, the majority of people cut on sleep, relying on that morning shot of caffeine to get energized. But getting a healthy amount of sleep means that the amount of deep sleep is gradually reduced throughout the night. This way, it’s much less likely you’ll be in deep sleep when it’s time to wake up. That’s why 8 to 10 hours of sleep per night is optimal for the majority of adults, both to avoid sleep inertia and restore metabolic potential.
  • Have consistent sleep and wake times. This will help maintain the body’s internal clock, ensuring that your sleeping and waking are not disrupted.
  • Wake up gently. Preferably, we should wake up without alarms – we would rise when our brain tells us to, having slept just the right amount of time and without risk of waking up during a stage of deep sleep. But this is obviously a luxury for most of us, and the best thing we can do if we have to use an alarm is to wake up gradually, with the alarm starting out quietly and ramping up over the next 10 minutes.

The suggestions we’ve given you for avoiding sleep inertia might sound like nothing new – but that’s what all the research points to. Time and time again, the science of sleep leads us to the same conclusion: listen to your internal clock and dedicate the time to establish the habits that will let it function smoothly. If we use the knowledge given to us and put in the effort to find what works best for us, we’ll be taking our days on with formidable strength. And it all starts with those first 15 minutes of the morning.