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Feeling groggy when you wake up? It could be sleep inertia

Posted on October 3rd, 2023

Do you ever wake up feeling like you’re in a fog, struggling to shake off that groggy sensation that’s hanging over you like a cloud? 

If so, you’re not alone. Many people experience this feeling upon waking, and it’s often attributed to something called sleep inertia. 

Here, you’ll learn what sleep inertia is, why it happens, and tips to minimize its effects. That way, you can start each day feeling refreshed.

What is sleep inertia?

Sleep inertia is the term used to describe the feeling of grogginess and impaired cognitive function that can occur after waking from a nap or a night’s sleep. It’s the transitional period between being asleep and fully awake, and it can last anywhere from a few minutes to several hours.

Symptoms of sleep inertia may include the following: 

  • Sluggishness and slow reaction times
  • A strong desire to go back to sleep 
  • Impaired visual attention 
  • Difficulty concentrating
  • Memory lapses
  • Mood swings
  • Impaired decision-making

Why does sleep inertia happen? 

The exact cause of sleep inertia isn’t fully understood, but researchers have three common theories: 

An increase in slow delta waves

Some studies suggest that sleep inertia happens due to an increase in slow delta waves in the back of the brain. These delta waves are common during deep sleep, and they become more active if you don’t sleep enough. 

Consequently, sleep inertia may occur if your brain hasn’t had a chance to slow down your delta waves before you wake up, or if you wake up abruptly during deep sleep. 

High adenosine levels

A compound called adenosine exists in your brain that affects your sleep. When you wake up, your adenosine levels should be low. But if they’re high, you may experience sleep inertia. 

Reduced blood flow to the brain

As you move through each sleep stage, the blood flow to your brain changes, either increasing or decreasing. Chronic fatigue syndrome (CFS) is a condition linked to reduced cerebral blood flow. It causes people to feel tired and demonstrate symptoms similar to sleep inertia. Therefore, some researchers speculate that reduced blood flow to the brain upon waking may lead to sleep inertia symptoms. 

Factors that may increase the likelihood and severity of sleep inertia include…

Sleep deprivation: Not getting enough sleep can make sleep inertia worse because your body hasn’t had the opportunity to complete its sleep cycles.

Sudden awakenings: Being jolted awake by a loud noise or disruptive alarm clock can trigger more intense sleep inertia.

Napping: Short naps are less likely to induce sleep inertia, but longer naps can leave you feeling groggy.

Individual differences: Some people are naturally more prone to sleep inertia than others, based on their genetics and sleep patterns.

How to minimize the occurrence of sleep inertia 

You can’t entirely eliminate sleep inertia. However, there are strategies you can try to minimize its impact:

Prioritize sleep: Ensure you get enough high-quality sleep by maintaining a consistent sleep schedule and aiming to get 7-9 hours of sleep per night.

Wake up gently: Avoid using harsh alarms that jolt you awake. Instead, ease yourself into consciousness by using gentler wake-up methods like…

  • A sunrise alarm that gradually increases your light exposure and uses gentle nature sounds
  • A smart alarm that registers when you’re in a light sleep stage

Nap strategically: If you need to nap, keep the nap short (20-30 minutes) to reduce the likelihood of falling into a deep sleep.

Establish a morning routine: Create a morning routine that involves light physical activity, hydration, and a balanced breakfast to kickstart your mind and body. Examples of good foods to eat for a more alert morning include the following: 

  • Oatmeal 
  • Greek yogurt
  • Eggs
  • Whole-grain toast
  • Nuts and seeds
  • Chia pudding 
  • Green tea

Avoid caffeine immediately upon waking: Contrary to popular belief, consuming caffeine right after you wake up may interfere with your body’s natural wakefulness process. Try waiting 30-60 minutes before reaching for your morning cup of joe.

Limit nighttime screen time: Exposure to blue light emitted by screens before bedtime can disrupt your sleep cycle, potentially exacerbating sleep inertia the next morning. 

Feeling groggy when you wake up is a common experience, and it’s often due to sleep inertia. Understanding why sleep inertia occurs and implementing strategies to lessen its effect can help you start your day feeling more alert and refreshed. 

Prioritizing good sleep hygiene and adopting gentle wake-up routines can go a long way in combating morning grogginess and setting a positive tone for the day ahead.

Dr. Meghna Dassani has practiced dentistry for over two decades and is passionate about the role dentists play in whole-body health. You can learn more at her website:

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