Forty to 110 minutes of deep sleep is recommended per night

The REM cycle—named for the 'Rapid Eye Movement' that occurs during this stage of intense dreaming—happens around four to six times per night.

Your brain moves through four distinct sleep stages every night

Each stage plays a key role in memory, repair, restoration, and other key biological functions. The full cycle generally proceeds from light sleep and deep rest into vivid REM dreaming, which repeats between three and five times nightly.

We dream for around two hours each night, on average, but the exact purposes of dreams remains under investigation.

How much sleep do you need?

When it comes to how much sleep you need, age matters—and, for your health, it's important to be well rested. Young children between the ages of one and three need the most sleep: It’s recommended that toddlers get between 11 and 14 hours of...

Humans may have evolved to need less sleep.

Sleepwalking, or somnambulism, is a bit of a misnomer since many things can occur during this state, including speaking, using the bathroom, and more.

Sleep is often viewed individually, when its impact and meaning may be more communal

At any given point, roughly 2 billion people may be asleep on Earth. The typical scientific description of sleep focuses on its individual impact, but the phenomenon shapes whole cultures and eons. This essay prompts a fresh rethinking of the importance of sleep for humanity.

The lost medieval habit of 'two sleeps'

While most people accept a single seven-to-nine-hour nightly slumber is ideal, the approach is a relatively modern idea. For centuries, interrupted sleep was the norm, with historians uncovering descriptions of two periods of sleep during the normal 24-hour cycle.

Delta brain waves happen during deep sleep, while REM cycles resemble being awake

As the brain cycles from wakeful rest to deep sleep, different brain waves emerge. Alpha waves occur during restful waking states, while theta waves can be associated with light sleep and meditation. Delta waves are observed during deep sleep—but REM cycles more closely resemble active awake states.

Some animals seem to live well on little sleep

African bush elephants typically sleep for about 2 hours per 24-hour day, coming in well under a human's recommended seven-hour minimum. Other animals also appear to skimp on sleep, by human standards, without the consequences humans associate with being sleep deprived. This academic article details the sleeping habits of animals that appear to thrive on fewer than 40 winks and explores whether their sleep processes are just built different.

High-quality sleep is effectively a superpower

Sleep is critical to maintaining healthy biological functions. From restoring energy to consolidating memories, aiding immune system functions and balancing hormone production, optimizing sleep habits are one of the most important ingredients to healthy living.

External factors, not aging itself, lead to sleep loss in older adults

Though it is often believed that people need less sleep as they age, the recommended sleep guidelines for all adult age groups are almost identical. However, factors such as medication use, lack of physical activity, and loneliness can lead to sleep problems, and thereby lead older people to believe that they actually need less sleep than they do.

Dreams largely occur during REM sleep (but not entirely).

A deeper walk through of the four stages of sleep

In this TED video, sleep expert Matthew Walker carefully breaks down the sleep stages along with a description of why each is important. He finishes the discussion by examining the consequences of altered or decreased sleep, and why seemingly small alterations in our sleep patterns can have outsized effects.

Sleep research published in 2021 confirmed that there is a 'creative sweet spot' when people are drifting off to sleep, and that if they wake up at that point to work, it can boost their creative problem-solving.

What sleep is for and why you can’t live without it

Sleep is one of the most important needs that humans have. The body uses sleep as a time of restoration and rejuvenation, as body tissues repair themselves, growth hormones are released, and the process continues. Brain plasticity theorists believe that sleep is also used for the processing and consolidating of new memories.

The brain will attempt to rest itself in periods of chronic sleep deprivation

Skimping on sleep lengthens reaction times and blunts decision-making skills. At a certain point, the brain will try to sneak sleep where it can, shifting sections offline even as you remain awake. Going without sleep raises blood pressure, undermines the immune system, and increases one's risk of dementia.

Studies suggest when you sleep is as important as how much you get.

A sleep expert discusses the broad benefits of quality rest

In this three-part series, renowned sleep expert Matthew Walker and doctor Peter Attia explore the role of sleep in memory consolidation and mental health, and the detrimental effects of chronic lack of sleep. The latter has been linked to increased risk of dementia, hypertension, and more.

About 10%-15% of people experience chronic insomnia

How often would you say you struggle to stay or fall asleep? If it's more than three times per week (and has been going on for at least one month), then you might have one of the most common sleep disorders: insomnia.

Cerebrospinal fluid flushes waste from your brain during sleep, performing a nightly brain cleanup that's an important purpose of sleep.

What happens when we sleep

Sleep is a highly specialized and complex process that begins via signals from a region of the brain called the hypothalamus. As explained in this overview video from The Economist, the hypothalamus maintains our circadian rhythm by using light cues from our environment to regulate sleep via a compound known as melatonin. Once asleep, the brain begins the "sleep cycle" and progresses through the four stages of sleep over and over again each night.

An estimated 1 in 250 people—a small subset of the population—reports they've never remembered a single dream.

Emerging research suggests that cannabis, used by about 9% of American adults as a sleep aid, may suppress rapid eye movement and lead to worse quality sleep and fewer remembered dreams.

Explore a series of bedtime exercises to improve sleep

Low-impact, mindful movements can potentially help the body and mind relax before sleeping. Such exercises could be a helpful complement to regular exercise during the day.

A third of US couples have opted for a 'sleep divorce'

A 2023 survey of roughly 2,000 US adults showed roughly a third of the participants opted to stay in a different room from their partner at night. Reasons for the so-called "sleep divorce" varied, from snoring issues to offset schedules. The survey, run by the American Academy for Sleep Medicine, also revealed the most sleep divorces within millennials. See the study for more on this change in sleep habits.

The brain consolidates memories during sleep

During sleep, the brain appears to process memories from the day and encode them into long-term storage. At the same time, the brain prunes old memories out of the brain that are no longer useful. Understanding this process also sheds light a various neurodegenerative diseases.

Understanding the stages of sleep

Do you have trouble keeping the different stages of sleep straight and organized in your mind? Us too. Sometimes it helps to have a straightforward listing of what each stage is and why it’s important. Look no further than this resource from Lumen. It is a basic outline of the four stages of the sleep cycle, along with the brainwaves and attributes that characterize each. If you’re brave enough, test yourself on the built-in quiz!

The human brain only uses 5% more energy during active tasks versus resting

Despite only being 2% of the weight of a human body, the average adult brain consumes 20% of its energy, with the majority of it spent on maintaining homeostasis—the stable equilibrium conditions of temperature, acidity, blood sugar, and other properties in the body. For infants, the consumption is closer to 50%.

People with a sleep disorder called REM Sleep without Atonia don't experience the temporary paralysis of skeletal muscles that typically occurs during REM sleep—instead, they have vivid dreams that they act out during sleep.

How to end bedtime procrastination

Finally done with external obligations, you might plop onto the sofa and dive into a hobby or bit of media, pushing past sleepiness to have some time to yourself and enjoy doing what you want. This is known as "revenge bedtime procrastination," a behavior that feels relaxing but impairs sleep hygiene.

Sleep is no longer considered a binary state—scientists are seeking to map a variety of liminal states between sleep and waking, including the hypnagogic state associated with boosts of creativity.

The evidence for the best sleep positions

For a behavior so crucial to human health, sleep positions are reportedly understudied by researchers. This article summarizes some of the more recent studies, taking into account the various forms of problems encountered during sleep: neck and back pain, snoring, acid reflux, and facial skin damage. Most studies point to side-sleeping as the most optimal, with sleeping on one's front as the least helpful. Read the piece to see which position is best for you.

Artificial lighting and modern practices like working late are linked with sleep shifts

An analysis of five adults participating in a German reality program that tasked them with living in a Stone-Age-like settlement for 2.5 months, provided some insights into how modern conditions may have shifted our circadian rhythms. The participants slept about 90 minutes more under these conditions, and went to bed earlier and rose earlier, raising questions about how circadian rhythms, sleep, and sleep quality are affected by modern lifestyles.

Olympians view sleep as a performance tool, prioritizing routine and environment

Elite athletes emphasize consistent sleep routines, dark and cool environments, the well-placed nap, and tools like eye masks, white noise machines, and supplements like melatonin (particularly for jet lag). This priority belies a core principle: recovery and performance are inseparable. Read more ways Olympians "sleepmaxx" here.

Obsessing over sleep metrics leads to worse sleep quality

Over one-third of Americans have used wearable technology to track their sleep, and the anxiety over having perfect sleep data, or orthosomnia, has made getting a good night's sleep more difficult. Experts agree that most devices cannot correctly assess sleep details, making the data unreliable.

Sleeping on a problem does seem to help—in fact research published in 2026 suggests scientists can seed people's dreams with sound cues about a difficult puzzle during REM sleep and they'll be better able to solve it.

Why don’t you remember all your dreams?

Despite being a near-nightly occurrence, we remember very few of our dreams. Researchers believe reduced activity in regions where memories are stored, a different neurochemical environment during sleep, and rapid transition during waking contribute to this phenomenon.

Similarities between human and animal sleep

Have you ever noticed the wide-ranging differences in sleep between humans and animals? Sleep as a necessity is present amongst all animal species, but the specific patterns of sleep vary widely. Just think of the differences between how an owl, a whale, and a horse might sleep. This helpful resource from the Sleep Foundation explores the relations between human and animal sleep, complete with some fascinating statistics about sleep patterns throughout the animal kingdom!

Circadian rhythms shift as we age—making older adults want to go to bed earlier

Throughout our lives our internal biological clocks shift. Early-to-rise toddlers become hard-to-wake teens and eventually early-to-sleep seniors. Circadian rhythm fluctuations throughout our life cycle explain some of these changes.

A quick technical overview of insomnia

Insomnia is one of the world's most common sleep disorders. Characterized by difficulties falling and staying asleep, long-term struggles with insomnia can prelude or contribute to health difficulties. Treatments range from sleep hygiene management and relaxation therapy, and medication, including antidepressants and melatonin.

Sleep training: risks and benefits

Sleep training, which can range from implementing a nighttime routine to letting your baby cry it out, is controversial, but does it work? While dozens of studies have found sleep interventions to be effective, it appears that many of these studies...

Sleep deprivation may slow metabolism

This article explains that, according to research from Penn State, restricting sleep for just a few days can affect how the human body metabolizes fats and change how satisfied people feel after a meal. The study found that people who don’t get...

It is recommended that humans consume 2.0 to 3.7 liters (about 4.2 to 7.8 pint glasses) of water daily to replace water lost through breathing, sweating, urination, and bowel movements.

The body's sleep-wake cycle is one of its many circadian rhythms

The body's sleep-wake cycle is one of its many circadian rhythms, which are behaviors or biological processes that exhibit 24-hour patterns. These rhythms are deeply impacted by light exposure, food availability, and much more, meaning where you live impacts your sleep.

Sleep apnea explained

While sleep apnea is directly tied to an increased risk of cardiovascular and metabolic health problems, many affected people are unaware of their problem. Sleep apnea occurs when upper airway muscles relax during sleep and pinch off the airway, which can cause breathing to pause for 10 seconds or more at a time. Sleep partners (rather than those inflicted) are often the first to notice breathing pauses or loud snoring in their bedmates.

The US loses roughly $400B a year in productivity due to sleep deprivation

For an article about a woman who built a business empire telling bedtime stories, the Hustle created this graphic showing the estimated GDP loss associated with chronic insomnia. The United States had a much more significant loss than other countries.

How dreams affect your memory

In 1999, scientists conducted a study in which participants were asked to recall images flashed before them for milliseconds. They found that participants who slept before recalling the information performed better than those who had been asked to recall the same information that same day. This was some of the earliest convincing evidence of how crucial sleep is for learning and memory, findings that current research continues to strengthen.

What it's like to live with insomnia

The biological process Shakespeare referred to as the chief nourisher of life's feast is necessary for the body and mind to rest and repair from the activities of daily life. As sleep evades the exhausted, sufferers also lose emotional stability, mental clarity, social connections, and more while simultaneously gaining waves of interrupted biological processes that can lead to disease and death.

Five patterns may define how we sleep—not just night owl or early bird.