Do you wake up feeling groggy? You may be suffering from Sleep Inertia!

12 Facts About Sleep Inertia


Do you ever feel so groggy after you wake up that you can’t wake up? Then you are probably experiencing what’s known as “sleep inertia.” Here are 12 facts about sleep inertia.


1. What is Sleep Inertia?

The majority of people who use a regular alarm clock often experience trouble waking up in the morning. Sleep Inertia often appears as the feeling of incomplete awakening and grogginess that reduces your ability to perform even simple tasks. Part of your body is actually still in a sleep state.

2. Sleep inertia costs you

Sleep inertia typically lasts 15-30 minutes, but can last as long as 4 hours. During this period, you are at a reduced level of capacity and may have trouble doing the simplest of everyday actions. In order to get rid of this state, most people rely on caffeine from their morning coffee or adrenaline from using loud alarm clocks.

3. The root cause of sleep inertia is clear

Sleep inertia is the result of sudden awakening during REM sleep. When you wake up during REM, you still have high levels of melatonin, causing sleepiness. The longer you sleep, the higher level of melatonin is observed during REM stage. When you wake up during non-REM sleep, your blood pressure, heart rate and brain activity are slowed down, helping you feel awake and alert much quicker.

4. The more you sleep… So what? Sleep inertia is still here.

Sleep inertia is dependent on several things, such as:

  • how long you have been asleep
  • the efficiency of your sleep
  • the stage of sleep at awakening

The longer we sleep, the more our body restores, and logically, sleep inertia should be reduced. However, when we get closer to awakening, the nature of our sleep changes creating new risks for sleep efficiency.

If any of your sleep stages is interrupted by sudden awakening, your sleep efficiency will be reduced. And on the contrary, there’s nothing better than awakening at the end of a sleep stage.

5. The human body doesn’t like to leave a job half-done

Think about sleep as of maintenance or recovery for your cells. Your body will be happier to leave you with 3 or 4 sleep stages completed rather than with 3 and a half.

6. Sleep inertia and regular alarm clocks are friends!

If you use regular alarm clock, your chances of sleep inertia can be as high as 89%.

Fixed-time alarm clocks wake you up the time you set it to, so it has no way of knowing what stage of sleep your body is in. It simply does what it can, and concerning the right moment for awakening, it just plays roulette. It’s hard to predict in which sleep stage you will be at 7AM the next morning.

Statistically speaking, there is a 45% chance that a fixed-time alarm clock will wake you up from REM sleep, and a 49% chance from non-REM sleep. These are your approximate chances to have sleep inertia. And there is only a 9% chance to be awakened around the optimal moment of sleep stage transition. You can play this roulette all your life and suffer from morning grogginess in the majority of cases.

7. Sleep inertia is dangerous

If you are awoken suddenly, the effects of sleep inertia can last from 30 minutes to 4 hours. During this period, you are most likely to make mistakes doing even well known routine actions. Sleep inertia has a wide range of unpleasant and definitely dangerous effects, affecting you and others:

  • Large amounts of caffeine affecting your heart
  • High adrenaline levels caused by loud alarm clock
  • Wake-up stress
  • Reduction in memory ability
  • Drowsy driving
  • Being late for work
  • Lower productivity in the first part of the day
  • Low performance and response time on tasks, loss of concentration
  • Impairment of the capability to make decisions

Some of these effects may be especially dangerous for bus drivers, pilots and other shift workers.

8. Sleep inertia and drowsy driving

Drowsy driving is estimated to cause about 20 percent of accidents. That is an estimated 1.2 million accidents a year, more than drugs and alcohol combined.

Many drowsy driving accidents occur early in the morning, not when the driver has been up too long, but when he or she has recently awoken and is still suffering from sleep inertia. Sleep inertia in a driver behind the wheel can be very risky as the impairment of motor and cognitive functions can affect a person’s ability to drive safely.

It is extremely important not to drive or operate machinery during any episode of sleep inertia. Your reaction time and level of concentration diminishes greatly during this time.

9. Even a short nap may result in severe sleep inertia

Sleep inertia can occur regardless of the duration of sleep. Disorientation can be experienced after a few seconds of sleep, a nap, or a long episode of sleep. Naps can leave people with sleep inertia, especially when they last more than 10-20 minutes. While sleep inertia usually only lasts for a few minutes to a half-hour, it can be detrimental to those who must perform immediately after waking from a napping period. Post-nap impairment and disorientation is more severe, and can last longer, in people who are sleep deprived or nap for longer periods.

10. Sleep inertia affects decision-making

Within the first 3 minutes of waking, decision-making performance can be as low as 51 percent of the person’s best decision-making ability before sleep. Decision-making performance may still be 20 percent below optimum performance as long as 30 minutes after waking. Sleep inertia may affect cognitive performance for up to two hours.

11. Traditional “old school” approach to fight sleep inertia

The most well-known “remedies” for sleep inertia are caffeine and adrenaline. However, these only help to overcome the consequences of sleep inertia, not the cause of the problem.

Caffeine and adrenaline stimulate the central nervous system, increasing wakefulness, and improving concentration and focus by boosting your heart rate and blood pressure.

12. Next Generation Approach: Prevent Sleep Inertia.

A regular alarm clock will go off at the preset time regardless of the sleep stage you are in, so if a regular alarm clock with a fixed time of awakening is the main reason for sleep inertia, the best option is to get rid of it. However in this case, there’s a risk of oversleeping. With its giant Christmas tree and party atmosphere, it is a fun and romantic spot for a winter proposal – Sleeping without any alarm may be also an extreme route, especially if you need to get to work in the morning.

There are several sleep stage alarm clocks that significantly simplify the life for their owners. These alarm clocks are aware of your sleep patterns and by waking you during optimal stages of sleep, can greatly fend off sleep inertia and improve how you feel first thing in the morning.

Related Articles: