What Is Somnolence? Why We Feel Sleepy

What Is Somnolence? Why We Feel Sleepy


What is somnolence? America’s #1 Sleep Doctor, Dr. Michael Breus has your answers about why you feel sleepy and how to get enough of it.

You are feeling verrry sleepy.

You can see why stereotypical top-hat-wearing, pocket-watch-wielding hypnotists say this instead of “You are feeling very somnolent.” It’s just not quite as catchy, is it?

But essentially, somnolence and feeling sleepy are the same things, according to our friends at Merriam Webster:

The quality of being drowsy; sleepiness.

Etymology fans will know that somnolence stems from the Latin root ‘somno’ meaning sleep, followed by an appropriate suffix. (If ever a sentence were to leave you feeling somnolent, that would have to be it. Yawn!)

But why do we feel sleepy in the first place? Why do we even need sleep? What’s happening to our bodies when we’re tired? And how can we make sure we get enough sleep?

Here’s where you can better understand the somnolence state:

Let’s find out with a bit of bedtime reading.

Woman sleeping in bed on her stomach

Is Somnolence a Sleep Disorder?

Short answer? No.

Somnolence in and of itself is not a sleep disorder. But it is a natural symptom of many sleep disorders. You don’t have to have a sleeping disorder to feel somnolent, and you don’t have to feel somnolent to be diagnosed with a sleeping disorder. 

Somnolence is distinct from hypersomnia or excessive daytime sleepiness (more severe symptoms of conditions like narcolepsy).

What are the most common sleeping disorders?

1. Insomnia

Insomnia is difficulty falling or remaining asleep despite wanting and having the time and space to do so. People with insomnia also experience excessive daytime somnolence and cognitive difficulties when they’re awake.

There are two major types of insomnia:

  • Sleep-onset insomnia – the classic ‘I can’t fall asleep’ kind.
  • Sleep maintenance insomnia – the ‘I can’t stay asleep’ kind.

It’s considered a chronic condition when symptoms occur at least three times per week for at least three months. 

Apparently, up to one-third of adults live with some form of insomnia.

2. Sleep apnea

Sleep apnea is multiple lapses in breathing while asleep. These temporary pauses in breathing affect the body’s oxygen supply, interrupting good-quality sleep and causing daytime somnolence.

There are two major types of sleep apnea:

  • Obstructive Sleep Apnea (OSA): when the airway at the back of the throat becomes physically blocked. 
  • Central Sleep Apnea (CSA): a problem with the brain’s system for controlling respiratory muscles. 

Sleep apnea is one of the most common sleep disorders and affects an estimated 2 – 9% of people of all ages and genders in the United States. 

3. Narcolepsy

Narcolepsy is severe and persistent excessive daytime sleepiness. Often misunderstood, narcolepsy is defined as chronic sleepiness that can cause difficulties at work, school, and social settings and increased risk of serious accidents.

Again, there are two major types of narcolepsy:

  • Narcolepsy Type 1: associated with cataplexy – the sudden loss of muscle tone and low levels of hypocretin-1 – a chemical that helps control wakefulness. 
  • Narcolepsy Type 2: absence of cataplexy, but can sometimes be reclassified as 

Narcolepsy is pretty rare. It’s estimated to affect about 20 to 67 people per 100,000.

While those three are probably the most well-known, there are several other sleep disorders, including:

  • Parasomnia
  • Restless Leg Syndrome
  • REM Sleep Behavior Disorder
  • Shift Work Disorder
  • Periodic Limb Movement Disorder
  • Somnambulism
Man sleeping in bed

Why Do We Get Sleepy?

Somnolence happens to everybody eventually. But what is going on? Why do we start to feel tired?

The best way to think about it is to think of the body as a battery. Just like your smartphone needs charging at night, so do you.

We instinctively know that we “run out of juice.” We talk about “putting fuel on the fire,” “gas in the tank,” or “recharging our batteries.” But what is this juicy gaseous battery fuel our bodies so dearly crave, and how does sleeping give us more of it?

When we stay awake for long periods, our brain starts telling us it’s time to wind down and recharge. It sends signals from several areas in the brain, including a structure called the suprachiasmatic nucleus (which sounds like something out of Mary Poppins).

This nucleus is located in the hypothalamus (a part of our brain that receives signals from our eyes). When our eyes see light, the brain gets signals that make us feel awake, and when it’s dark, the signals make us feel tired.

This is our natural circadian rhythm, which works like a clock in the body. It’s this clock that controls the production of melatonin, a hormone that helps tell your body when to sleep and when to wake up. 

When your body releases more melatonin, you feel more tired. As the light fades, the human body starts releasing melatonin and continues throughout the night. Then, the body slowly stops decreasing melatonin in the morning.

You can see how modern life, with electric lights and oh so many screens, can easily interfere with your body’s natural sleep patterns. This is why Mindvalley’s Sleep Doctor, Michael Breus, recommends ending screen time early and keeping your room as dark as possible.

Why Do We Need Sleep?

Surprisingly, it’s still not easy to get a plain answer out of people on this one. While we know many of the benefits of getting sleep and the dangers of not getting enough, we don’t know precisely why we (and other mammals) sleep.

From an evolutionary perspective, sleep must be crucial because it puts us and our four-legged counterparts in a very vulnerable state. And not sleeping is, in fact, deadly. In one study, rats who were deprived of sleep lost weight despite having more food and died after a few weeks.

Neuroscience tells us that one function of sleep is to replenish brain glycogen levels, which diminish during waking hours. 

What’s certain is that sleep is crucial for neurological development and cognitive function. 

The fact that infants require up to 16 hours of sleep and teenagers require upwards of 9 hours could provide the biggest clue that the brain simply can’t do all its rewiring and processing while supporting waking consciousness.

Benefits of Sleep

The health benefits of getting enough sleep are well documented, but if you’re having trouble with any of the following, you might benefit from reexamining your sleep routine:

  • Sleep helps control our metabolism and weight
  • Promotes stable moods
  • Helps prevent cardiovascular diseases
  • Boosts our immune system/function 
  • Increases knowledge retention
  • Helps with long and short-term memory
  • Essential for brain function
Man kissing woman on forehead in bed

How to Stop Feeling Sleepy

So what can we do about somnolence? One of the best ways to tackle feeling sleepy is to optimize your sleep habits.

If you want to get a consistently good night’s sleep, there are several simple things you can do.  We teamed up with America’s #1 Sleep Doctor, Dr. Michael Breus to help.

From knowing when to stop drinking caffeine, choosing the proper bedtime, and knowing how much sleep you need according to your specific sleep chronotype, Dr. Breus will open your eyes to how best to close your eyes.

Watch the First Lesson of the Quest

Dr. Michael Breus, Ph.D is America’s most trusted Sleep Doctor, teaches the mastery of sleep

Discover why the world’s top performers sleep an extra 90 minutes more than the average person, and discover a five-step formula for the best sleep of your life.Get started for free

Written by
Matt Coates