Sleep Inertia

Last Updated: September 18, 2023

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Consistently falling asleep after an alarm goes off, trouble getting out of bed, and long-lasting grogginess? Sounds like sleep inertia. Sleep inertia is the tiredness that persists after waking up. Some short-term grogginess is normal, but long-lasting sleep inertia can negatively impact daily life.

What is Sleep Inertia?

Sleep inertia is the period of tiredness that occurs upon awakening. Sleep inertia is present during the transition from sleep to wakefulness and for some time after waking up.

Effects of sleep inertia include impaired cognitive performance and poor perceptual and motor skills, reduced coordination, illogical reasoning, poor problem-solving ability, and general feelings of brain fog.

Experiencing sleep inertia is normal, and the duration and effects vary greatly between people.

Sleep Inertia Length

Experiencing sleep inertia is normal, and the duration varies from person to person. Most cases of sleep inertia last from as little as two minutes to a full hour after waking up, but sleep quality, circadian phase, and sleep cycles can all change the duration.

The Impacts of Sleep Inertia

Sleep inertia's physical, psychological, and mental effects can impact daily life. Some people will show more sleep inertia than others, and those with severe sleep inertia may show longer-lasting symptoms, including:

  • Reduced or impaired cognitive performance
  • Poor perceptual and motor skills
  • Reduced reaction time
  • Inability to perform safety-critical tasks
  • Psychomotor vigilance deficits
  • Reduced attentional processes

Sleep inertia can have profound negative impacts on people who need to make fast decisions or perform safety-critical tasks immediately after waking, like firefighters or emergency response personnel.

For this reason, much research is now aimed at finding ways to reduce sleep inertia and improve performance immediately after waking. The negative impacts of sleep inertia are well-documented.

Symptoms and Associated Conditions

Brain Fog and Confusion

The most notable effects of sleep inertia are brain fog, disorientation, or confusion upon awakening.

Brain fog is described as dissociation, forgetfulness, or extra cognitive effort when performing even basic tasks.

Alertness and Performance

Reduced alertness and performance might be the most dangerous effect of sleep inertia.

Especially in cases where someone needs to perform immediately upon awakening, like a firefighter or soldier, the reduced coordination, increased reaction time, and lessened vigilance that accompany sleep inertia can put their own life or the lives of others at risk.


A general feeling of tiredness may linger after other sleep inertia symptoms dissipate. Sleep inertia affects how long tiredness will last upon awakening, and prolonged sleep inertia symptoms can include long-last tiredness throughout the day.

Sleep Drunkenness

Sleep drunkenness is often observed alongside sleep inertia.

While sleep inertia generally refers to tiredness and lowered performance, sleep drunkenness is a form of parasomnia - an unusual sleep-related phenomenon – when the body is up and moving, but the brain is still transitioning to wakefulness.

Causes of Sleep Inertia

The exact causes of sleep inertia are still under study. Many factors that increase sleep inertia have been identified, but further research is needed to determine what causes sleep inertia.

The following causes are known to increase sleep inertia severity, but the exact combination of causes is not yet known.

Poor Sleep Hygiene

Sleep hygiene is a broad term for general sleep health and habits. Good hygiene involves falling asleep and waking up consistently, maintaining a regular biological night, keeping a clean bedroom, avoiding blue light and entertainment before bed, and focusing on sleep quality.

Poor hygiene can increase the duration of sleep inertia and make symptoms worse. To avoid sleep inertia, focus on developing healthy sleep habits and good sleep hygiene.

Sleep Deprivation

Sleep-deprived people are more prone to experience sleep inertia. Studies have found that prior sleep deprivation, or sleeping too little on previous nights, can make sleep inertia much worse.

A short nap while sleep-deprived can also cause more intense sleep inertia symptoms.

Abrupt Awakenings

Being rocked awake from a deep sleep can leave someone feeling groggy and disoriented for much longer than gradually waking up with a natural circadian rhythm. The body passes from light to deep sleep and back several times in a good night’s sleep.

Waking in one of the deeper sleep stages, especially NREM3 or slow wave sleep, increases the chances of sleep inertia occurring.

Abruptly waking outside a lighter stage dictated by the body’s circadian rhythms can disrupt the brain’s natural sleep-wake processes and cause sleep inertia.

Disrupted Sleep Patterns

A consistent sleep schedule with a regular bedtime and wake-up time can reduce sleep inertia. The opposite is also true - night shift workers, new parents, and people with trouble falling asleep often report higher sleep inertia.

The circadian rhythm, or the body’s natural, internal sleep-wake cycle, governs when and how the body sleeps and wakes.

Disruptions to that circadian rhythm, like irregular sleep schedules and disrupted sleep cycles, worsen sleep inertia.

Sleep Disorders, Insomnia, and Sleep Apnea

A sleep disorder can worsen sleep inertia by disrupting the natural progression from one sleep stage to the next.

Frequent waking, shallow sleep, difficulty falling or staying asleep, and daytime sleepiness can all result from a sleep disorder, which can all induce sleep inertia.

Because symptoms of sleep disorders are often similar to sleep inertia, the conditions frequently overlap.

Medications, Supplements, and Nutrition

Proper nutrition and supplementation can improve sleep quality. A diet rich in zinc, magnesium, and vitamins B and D helps maintain sleep, and deficiencies in these nutrients may contribute to sleep inertia.

Additionally, some medications or drugs that cause disorientation or drowsiness, like alcohol, marijuana, or sleep medicine, may cause prolonged sleep inertia after waking up.

Other Conditions and Contributors

Studies have identified dozens of other contributing factors to sleep inertia, with varying degrees of impact. Some of these include:

  • Obstructive sleep apnea: when breathing abruptly starts and stops during sleep.
  • Delayed sleep phase syndrome, where the sleep schedule is interrupted, and a person cannot sleep and wake during “normal” hours.
  • Stimulant medications that may impact the sleep schedule.
  • Sedative medications, including sleep medicine, can interrupt the progression through the sleep stages.
  • Insomnia or difficulty falling asleep.
  • Narcolepsy, excessive daytime sleepiness, or sudden sleep attacks, regardless of prior sleep.
  • Non-sleep disorder conditions that may impact sleep quality, like restless leg syndrome, periodic limb movement syndrome, or nocturnal epilepsy.
  • Other sleep disorders: any sleep disorders with homeostatic and circadian influences that can reduce someone’s chances of getting high-quality sleep.  

Sleep Stages and Sleep Inertia

During biological night - the period when a person gets their “nighttime sleep” regardless of their sleep schedule - people experience four distinct sleep stages, known as the sleep cycle:

Non-REM 1 and non-REM 2

Non-REM 1, N1, is the transition from wakefulness to sleep. This is the lightest sleep stage, drifting between being awake and sleeping. This stage typically lasts a few minutes and is often the only stage reached in a short nap. Waking during Non-REM 1 does not cause sleep inertia.

Non-REM 2, N2, is a slightly deeper stage of sleep characterized by reduced brain activity and decreased body temperature. Over 50% of total sleep time is normally Non-REM 2. Sleep inertia does not occur when waking from Non-REM 1 and is unlikely, but it can occur if waking in non-REM 2

Non-REM 3, Deep Sleep, or Slow Wave Sleep

Non-REM 3, N3, is the deepest stage of non-REM sleep. It is also known as deep sleep or slow wave sleep. N3 is the most restorative stage of sleep for physical growth and healing. During N3, the brain produces fewer beta waves and more slow delta waves, and cerebral blood flow velocities decrease greatly.

This decrease in brain activity leads to slower brain reactivation, meaning a person is more likely to experience sleep inertia when waking from Non-REM 3 than any other sleep stage.

REM Sleep

REM Sleep, or rapid eye movement sleep, is the last stage in the sleep cycle. This stage is characterized by heightened brain activity and the presence of dreams.

Waking during the middle of REM Sleep may cause sleep inertia, but the transition from REM to N1 is generally considered the best time to wake up to avoid sleep inertia.  

Sleep stages are characterized by the brain’s blood flow, the presence of beta and delta waves, brain activity, core body temperature, and more. Waking from one of the deeper sleep stages is more likely to cause sleep inertia.

Essentially, the deeper the sleep, the harder it is to wake up. A short nap that doesn’t get deeper than N1 will not cause sleep inertia - but waking after a lengthy sleep period can be a challenge, especially if an alarm goes off in the middle of Non-REM 3.

Diagnosing Sleep Inertia

Most people experience some level of sleep inertia, and it is normally not a problem. In some severe cases, though, sleep inertia effects may warrant a diagnosis and treatment intervention.

A sleep specialist is the best option for a diagnosis, but a general practitioner can likely provide the diagnosis if needed. Sleep inertia diagnoses often involve a sleep test, questionnaire, and subjective self-reports.

Clinical studies have used electroencephalographic sleep inertia measures to look at cerebral blood flow in the waking brain, but these tools are generally not used in a normal diagnostic process.

Dealing with Sleep Inertia: Tips, Tricks, and Treatment

There are many options to address the effects of sleep inertia at home without seeing a sleep specialist or acquiring a diagnosis. Reducing contributing factors of sleep inertia will promote better, more restful sleep and prevent sleep inertia.

Sleep Stage Manipulation

Working to wake up in one of the sleep stages closest to being awake is the most recommended method of reducing sleep inertia.

A Good Night's Sleep

Avoiding sleep deprivation improves sleep inertia symptoms, too, with people reporting a shorter duration of sleep inertia after a lengthy sleep period than people subjected to sleep restriction or sleep deprivation.

Proper Sleep Hygiene

It may seem obvious, but good sleep hygiene - the set of practices that promote sleep health and habits - reduces the effects of sleep inertia. These are things like keeping a clean sleeping area, limiting screen time before bed, and avoiding bright light in the sleeping area.

Smart Alarms

Some alarms work with wearable technology or smartphones to measure the depth of breathing and body temperature to determine the best time to wake up in the sleep cycle. These alarms are exceptional tools to avoid sleep inertia.

Frequently Asked Questions

Is Sleep Inertia The Same As Sleep Drunkenness?

Sleep inertia and sleep drunkenness are often experienced together but have different symptoms. Inertia normally involves slower reaction time and feelings of grogginess, while drunkenness is characterized by confusion and disorientation.

I Have Sleep Inertia. What Should I Do?

If you are experiencing sleep inertia, the first step is to look at your sleep habits and hygiene. Aim to fall asleep consistently every night, and use a smart alarm app to wake you up at an ideal time in the sleep cycle.

Does Caffeine Help Sleep Inertia?

Caffeine can help reduce sleep inertia symptoms, but sleep inertia has normally passed by the time caffeine begins to work. Studies have found mixed results, with caffeine being most effective if taken immediately after waking up.


Sleep inertia - Wikipedia

Sleep Inertia: Causes, Symptoms, and Treatment | Sleep Foundation 

Time to wake up: reactive countermeasures to sleep inertia 

Waking up is the hardest thing I do all day: Sleep inertia and sleep drunkenness - PMC 

On-call work and sleep: the importance of switching on during a callout and switching off after a call - PMC 

Caffeine eliminates psychomotor vigilance deficits from sleep inertia 

Focusing on a biological night: towards an epidemiological measure of circadian disruption | Occupational & Environmental Medicine 

Sleep inertia - ScienceDirect 

Electroencephalographic sleep inertia of the awakening brain | Neuroscience

Why Is Waking Up So Hard? 


The contents of this article are provided for informational purposes only and are not intended to substitute for professional medical advice, diagnosis, or treatment. It is always recommended to consult with a qualified healthcare provider before making any health-related changes or if you have any questions or concerns about your health. Anahana is not liable for any errors, omissions, or consequences that may occur from using the information provided.