An Overview of Sleep Inertia

Some people wake up in the morning and find that, even though their body is in motion, their brain doesn't seem to be keeping up yet.

People who still feel groggy for a while after they get up may be experiencing sleep inertia. It's not quite the same thing as simply having a poor night's sleep and feeling tired as a result.

This article explains what sleep inertia is and how it was discovered. It offers details on the sleep science behind the symptoms of sleep inertia and some steps you can take to better avoid them.

Sleep inertia was first identified among U.S. Air Force pilots during the 1950s. Pilots were often in the cockpits of their planes when on duty so that they'd be ready to take off at a moment’s notice.

What military officials discovered was that these pilots made simple mistakes if they were asleep when the alarm sounded and they sprang into immediate action. Even though they were awake, they couldn't perform tasks at their best until their minds caught up too.

Inertia refers to a concept in physics. It finds that an object naturally resists changes in its state of motion. A ball rolling down a hill will continue to roll, based on the principle that a body in motion stays in motion. A body at rest will stay at rest unless other forces act upon it to alter this state.

Symptoms

Sleep inertia leads to sleepiness that you're slow to shake off. You may have trouble thinking straight or understanding information right after you wake up. You may feel clumsy or absent-minded as the messages from your brain that control motor skills are slow to reach your body.

Though most of us aren’t flying fighter jets, we may be impaired in our ability to make decisions or perform complex activities.

For example, it may be difficult to drive a car safely right after you awaken. You may forget that you already poured your juice, or you may put your shoes in the wrong place without thinking. Your mental state may even keep you in bed with nothing more than a strong desire to return to sleep.

Causes

Symptoms of sleep inertia most often occur with a sudden or abrupt awakening. That's especially true if you are in a deep or slow-wave sleep stage in the first part of the night. It's also more likely when you simply haven't slept long enough.  

Sleep inertia symptoms may last for a few minutes or up to an hour or more. One theory suggests that it is caused by a neurotransmitter, or chemical messenger, called adenosine. It may build up in the brain during non-REM sleep and cause you to feel sleepy.

Sleep disorders, such as sleep apnea and delayed sleep-wake phase disorder, may make matters worse. Sleep apnea disturbs the quality of sleep with small, frequent interruptions to restore breathing. Other symptoms of sleep apnea may include:

• Snoring
• Gasping or choking episodes
• Witnessed pauses in breathing
• Frequent urination at night
• Teeth grinding
• Insomnia including early morning awakenings

Insomnia is a key symptom of delayed sleep-wake phase disorder. It is paired with a delayed natural ability to fall asleep at the beginning of the night. The "night owl" pattern often starts in the teen years but may last through a lifetime. 

Someone with this disorder may not fall asleep until 2 A.M. or later. It's then hard to wake up in the morning.

Idiopathic hypersomnia, or sleepiness of an unknown cause, may also contribute to sleep inertia.

Treatment

The first step in treating sleep inertia is to make sure you get enough quality sleep. Most adults need seven to nine hours of sleep each night to feel rested. Older adults may get by on a little less sleep.

You'll also want to be sure that any other sleep disorders, like sleep apnea, are treated. Your healthcare provider or a sleep specialist can diagnose a disorder. They can recommend treatment, such as continuous (CPAP) or bilevel (BiPAP) positive airway pressure.

Treatment for an underlying sleep disorder is likely to reduce your sleep inertia episodes. Some people may want to try using an alarm that wakes them up within a range of times. The alarm will prompt an awakening when light sleep or movements are noted.

Exposure to morning sunlight can be an effective way to feel more refreshed when you awaken. It helps your body to send the signals that maintain your circadian rhythm, or personal "body clock." These signals are key to how your sleep-wake cycles work.

As a last resort, caffeine may help. So can prescription stimulant drugs like Nuvigil and Provigil, used to promote wakefulness in the morning.

Summary

Sleep inertia happens when you wake up in the morning but feel your mind isn't clear until a bit later. The exact cause is still unknown but other sleep disorders may be at work.

In some cases, the symptoms of sleep inertia may emerge when you wake up suddenly from a deep-sleep stage in the sleep cycle. In others, sleep apnea or another sleep disorder may contribute to sleep inertia.

If your episodes of sleep inertia are not rare, speak with your healthcare provider about getting a sleep test or other evaluation. They may reveal a sleep disorder that, once diagnosed and treated, may relieve your sleep inertia symptoms.

A Word From Verywell

There's much you can do to avoid sleep inertia symptoms. Set up your sleep schedules and spaces so that they give you the best chance of getting a good night's sleep. Limits on your evening screen time, or any caffeine use late in the day, are simple changes that may help.