Sleep Inertia: Causes, Symptoms, and Diagnosis

by Lee A. Surkin, MD, FACC, FCCP, FASNC, FAASM

Have you ever woken up in the morning with an intense urge to go back to sleep even after getting the recommended amount of sleep per night? Do you experience morning grogginess when this happens to you? This phenomenon is what’s known as sleep inertia and although it itself isn’t a bad thing, it can harm cognitive functions and potentially cause other problems if it becomes severe.

Continue reading below to find out what causes sleep inertia, sleep inertia symptoms, and how it is diagnosed.

“Sleep inertia is most common in people who work long hours or shift work and can negatively affect their safety and well-being.”

Sleep Inertia Basics

In short, the feeling of morning grogginess, drowsiness, cognitive impairment, and sleep drunkenness is called sleep inertia. It typically lasts for 15 minutes to an hour, but in more severe cases it can last for up to a couple of hours upon waking up.

The biological reason why some people experience sleep inertia symptoms hasn’t been determined yet, but experts guess that it helps in maintaining sleep when unwanted wakings occur. So, sleep inertia is thought of as a protective mechanism.

Sleep inertia is most common in people who work long hours or shift work and can negatively affect their safety and well-being. Due to morning grogginess and sleep drunkenness, these people have a slower reaction time and reduced cognitive alertness.

Sleep Inertia Symptoms

Generally, the most noticeable sleep inertia symptoms present right after waking up and slowly disappear over time. Now, let’s have a look at the most common symptoms of sleep inertia:

• Morning grogginess
• Sleep drunkenness
• An urge to go back to sleep
• Poor cognitive ability
• Impaired visual attention
• Reduced spatial memory

What Causes Sleep Inertia?

We already mentioned above that researchers haven’t determined the exact biological cause of sleep inertia. However, according to research, three common theories may explain what causes sleep inertia.

First, it is believed that sleep inertia is caused by increased delta waves in the posterior part of the brain. These waves are also called slow waves and are part of the NREM (non-rapid eye movement) sleep stage and usually increase after periods of lack of sleep or sleep deprivation. So, when the brain hasn’t reduced these waves to prepare for waking up or is awoken during the NREM sleep stage, sleep inertia may occur.

The second potential theory explaining what causes sleep inertia is the adenosine theory. Namely, adenosine is a nucleic acid compound in the brain that is key for sleep and wakefulness. The levels of this compound should be low after waking so if they remain high it may lead to experiencing sleep inertia symptoms.

Third, based on the stage of sleep, sleep cycles determine the pattern in which blood flows to the brain. One syndrome called CFS (chronic fatigue syndrome) is very similar to sleep inertia and is linked to decreased cerebral blood flow. It is possible that the blood flow reduction after waking leads to sleep inertia symptoms.

Sleep Inertia Diagnosis

If you experience morning grogginess, sleep drunkenness, or other sleep inertia symptoms, ensure you consult your doctor and consider doing a polysomnography sleep study. This will help your doctor see whether or not there’s an underlying sleep disorder affecting your sleep and causing sleep inertia.
Another way to help your doctor diagnose you with sleep inertia is keeping a sleep journal to get an insight into your sleeping patterns. That said, you should take records of the times and the amount you sleep as well as how you feel upon waking and whether or not you experience any symptoms.