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

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.

Sleep paralysis occurs when the body fails to 'unfreeze' in sync with waking.

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.

Narcolepsy occurs when the brain loses its ability to control its sleep-wake cycle.

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

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.

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.

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.

Why do we sometimes jolt awake before falling asleep?

Around 70% of people are estimated to experience the sensation of falling and jerking awake right as they're about to drift to sleep. That mysterious phenomenon is called hypnic jerking. As common as it is, hypnotic jerking remains disconcerting and hard to explain. While we don't yet have clear answers, peruse this article in Popular Science for some possible explanations as to why this happens.

Forty to 110 minutes of deep sleep is recommended per night

Adults typically spend 10% to 20% of the night in deep sleep, also known as slow-wave sleep, with the rest of the night spent either in light sleep or REM states.

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.

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

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.

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.

Why do dreamers twitch?

This thought-provoking piece highlights newer research suggesting sleep twitches may not be random dream leftovers, but instead a crucial way our brains map and understand our bodies. From sleeping rat pups to dreaming octopi, this biological mapping system appears universal across animal species.

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

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.

Sleep disorders can exacerbate neurological and other health conditions

Brain regions that control sleep sit adjacent to those that regulate the autonomic nervous system, which controls involuntary bodily functions like heart and breathing rates. These neighbors influence each other, meaning poor sleep can impair or negatively impact the ANS, further disturbing sleep.

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.

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.

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.

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.

Animal brain studies show brain activity similar to what we'd expect during dreams, but parsing whether animals are truly dreaming depends on how one defines dreaming and how scientists could prove it.

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!

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.

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.

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.

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.

Dream interpretation has evolved from ancient mystical explanations, to dream reports, to tracking electrical activity in the brain and more.

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.

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.

The overlooked physical causes of insomnia

Persistent lack of sleep is dangerous for anyone, but women are especially unlikely to have their symptoms taken seriously. This article highlights the physical causes of insomnia—a condition often written off as solely psychological—and the importance of early diagnosis. The writer, Courtney Maum, was diagnosed with an anterior nasal valve collapse as the source of her insomnia.

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.

How your subconscious influences your decisions

How much of your desires and daily choices are truly yours? One of the most effective ways to influence someone's subconscious is when they're asleep. To study this possibility, researchers trained participants to be able to dream lucidly, a phenomenon that occurs when a dreamer knows they're dreaming.

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.

Poor sleep increases the risk of developing Alzheimer's, and a main reason appears to be that the brain disposes of toxic protein buildup during high-quality sleep.

Roughly 1 in 5 people experience lucid dreaming at least once a month—that's the ability to control or influence your dream environment.

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

During dream sleep, the brain connects new information learned during the day with information already stored in the mind, creating a revised mind-wide web of associations.

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.

Sleep research indicates dogs likely dream about their toys, food, and owners.

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.

A closer look at why people snore

Snoring is simply noise caused by improper airflow during sleep—and while it’s something that most people will do at some point in their lives, it can also be indicative of larger health problems. Generally speaking, snoring occurs when soft...

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.

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.

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!

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...

Nightmares are unpredictable, but are linked to stress, anxiety, trauma, and more.

The body's response to cardiac arrest has been linked to near-death experiences.

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.