Top 10 Scary Facts While Sleeping: What You Need to Know

Sleep is meant to be a peaceful respite from our wakeful reality. However, many creepy, unsettling, and downright scary things can sometimes occur while we slumber. From paranormal phenomena to bizarre medical disorders, these top 10 scary facts about sleeping are sure to make your hair stand on end.

1. Sleep paralysis

is a temporarily terrifying experience that occurs when you are conscious and awake but unable to move or speak. It happens when the brain awakens before the body’s REM sleep paralysis has ended, leaving you fully conscious but still paralyzed.

The physiology behind it relates to REM (rapid eye movement) sleep, the stage when most vivid ai dedreaming occurs. During REM, your pons in the brainstem paralyzes your muscles through motor inhibition to prevent you from acting out your dreams. Usually, this temporary paralysis goes away by the time you are fully awake and conscious.

However, in sleep paralysis, you become aware before the paralysis wears off — rendering you stuck and frozen in a frightening state unable to move your body, head, or vocal cords no matter how hard you try. This typically lasts around a minute or two as your body catches up, but it can feel like an eternity spent powerlessly trapped in your paralyzed body.

Making the experience even more frightening, many people report hallucinations of shadowy human figures, dark entities, or evil presences lurking during their sleep paralysis episodes. While these visions are not physically real, they can feel vividly real at the time due to the unique semi-awake/semi-sleeping state of sleep paralysis blurring reality.

The hallucinations likely relate to REM’s dream imagery mixing with waking consciousness, as well as potential influences of pre-existing fears, supernatural beliefs, or narratives from one’s culture about spirits or demons. Sleep paralysis visions tend to be shaped by the person’s particular anxieties and worldview.

While undeniably terrifying, sleep paralysis is not physically dangerous and the hallucinatory visions quickly vanish once the temporary paralysis ends and you can move again. However, the experience can cause lingering anxiety, especially if it occurs frequently. Managing stress, sleep habits, and psychiatric conditions like sleep apnea may help prevent recurring sleep paralysis for some individuals.

2. Sexsomnia

Sexsomnia, also called sleep sex, is a distinct type of parasomnia involving unconscious sexual behavior during sleep. People with sexsomnia will engage in sexual acts like masturbation, fondling, sexual vocalizations, or even initiating sexual intercourse with a partner while they remain in a semi-awake state of slumber.

The behaviors can range from mild to severe, including aggressive or violent sexual movements and actions. What makes it particularly distressing is that sufferers have no recollection whatsoever of their nocturnal sexual actions upon fully waking up.

This disruptive disorder is more commonly experienced by men, but can occur in women too. Potential triggers include sleep deprivation, stress, sleep apnea, fatigue, medications that affect sleep cycles, and substance use. It tends to emerge in adulthood but can occur in teenagers as well.

From a neurological perspective, sexsomnia arises from a dysregulation between the brain’s amygdala (involved in sexual behavior) and frontal lobe areas controlling arousal and awareness during specific phases of non-REM sleep. It causes certain sexual behaviors to manifest physically while the sufferer remains in a largely unconscious, dissociated state of slumber.

Not only embarrassing for the person exhibiting the disorder, sexsomnia can also prove highly traumatic for any unknowing romantic partners who find themselves on the receiving end of unconscious and non-consensual sexual actions during the night. It can severely disrupt relationships and personal boundaries.

Treatment typically involves improving sleep hygiene, avoiding precipitating factors, using sedatives carefully if needed, and potentially sleep medication or psychotherapy. For some, self-adopted preventative measures like sleeping separately, sleep monitoring devices, or sleeping with the arms constrained may be recommended as well.

3. Night Terrors

Night terrors are dramatic episodes of extreme terror, panic and screaming while sleeping that can last minutes and are very difficult to wake someone from. They are classified as a parasomnia disorder involving dysregulation of the brain’s sleep-wake cycle.

Night terrors typically occur during the transition from the deeper stages of non-REM sleep to lighter REM sleep, usually 2–3 hours after initially falling asleep. They cause abrupt bouts of intense fear, screaming, thrashing around violently, increased heart rate, perspiration, and feelings of dread — despite the sufferer’s eyes being open.

Unlike nightmares which are vividly recalled dreams, those experiencing night terrors have no recollection of actually dreaming or the source of their extreme terror upon awakening. They just feel an overwhelming sense of fright, usually unable to reassure or comfort themselves.

Night terrors most commonly affect children aged 3–12, with a peak around 3.5 years old. However, they can persist into adolescence and adulthood as well. Fatigue, anxiety, fever, and disruptive sleep schedules may trigger episodes in those predisposed.

From a biological standpoint, night terrors are thought to be caused by an over-activation of the brain’s limbic system (which controls fight-or-flight emotions) during sleep stage transitions. This hyperarousal prompts a flood of adrenaline when falling into or out of deep non-REM sleep.

Night terrors are more than just bad dreams — they are scary, screaming overreactions where the brain gets “stuck” between being asleep and awake. This disruptive disorder can be traumatic for both sufferers and anyone witnessing the disturbing episodes.

While night terrors resolve on their own as the brain’s sleep/wake cycles mature, ensuring safety is important during episodes. Letting night terrors run their course without trying to wake the person is recommended. Good sleep habits, schedules, and avoiding triggers like stress may help reduce frequency over time.

4. Somniloquy

Somniloquy refers to the act of speaking or vocalizing during sleep. It is essentially talking aloud while in a slumbering state, often uttering gibberish, nonsensical phrases, or even carrying on full conversations.

Mild sleep talking is very common, affecting around 5% of adults and even higher percentages of children to some degree. Mumbling a few words here and there during the lighter sleep stages is generally considered normal and harmless.

However, some people experience severe and excessive somniloquy, where they vividly vocalize for extended periods during slumber. This can range from providing clear commentary about their dreams to shouting, arguing, cursing, or even giving lengthy monologue-like speeches and lectures — all while remaining fully asleep.

In extreme cases, somniloquists have been known to carry on bilateral conversations covering complex topics like academics, politics, or storytelling — shouting questions and answers back and forth to themselves while others listen in astonishment nearby.

The unusual vocal behaviors of somniloquy stem from a disconnect between the brain’s sleep and wakefulness pathways. During REM sleep when most vivid dreaming occurs, the muscles responsible for speech are not issued the usual paralytic signal. This allows the speech muscles to physically ventriloquize the dream’s auditory experiences.

While typically benign, somniloquy can be problematic for bed partners being unceremoniously awoken by loud shouting or rambling speeches in the middle of the night. It can also be disturbing for the uninitiated to witness a “sleep talker” appear to be consciously conversing despite being dead asleep.

Somniloquy exists on a spectrum from mild sleep mumbles to full-blown vocal outbursts and dissertations. For most it is an odd but harmless quirk. But in rare and severe cases, it could potentially be a manifestation of an underlying sleep disorder warranting medical evaluation.

5. The Incubus

The incubus is a legendary evil entity or demon that goes back centuries across various cultures and folklore traditions. Tales depict the incubus as a malevolent male figure or presence that lies upon people in their sleep, immobilizing and sometimes assaulting them.

The earliest known references to incubi (plural form) date back to Mesopotamian and Hebrew texts over 4,000 years ago, which warned of these evil spirits that would terrify and molest women during the night. The incubus myth expanded into Christian demon lore during the Middle Ages, coinciding with the societal persecution of accused witches.

Descriptions vary, but the incubus is often portrayed as a demonic being with an ugly, frightening appearance that takes the form of a human, animal, or supernatural entity. It is said to forcibly hold down and immobilize the sleeper, sometimes scratching, biting, or engaging in sexual attacks and violations.

While obviously rooted in archaic superstition, the incubus phenomenon bears similarities to the modern experience of sleep paralysis. During sleep paralysis, people report feeling an evil presence and visions of shadowy figures lurking near them while their bodies are frozen in a temporary paralytic state.

This has led many psychologists and folklorists to theorize that incubus legends emerged from the terrifying visions and physical paralysis of sleep paralysis — especially the hallucinatory sense of a malevolent force holding one’s body down. These waking dreams were likely interpreted through existing cultural beliefs about demons in past eras.

Whether the stuff of myths and night terrors or grounded in real parasomnias, the ominous incubus has persisted as an iconic piece of paranormal lore encompassing the vulnerability of sleep and humankind’s subconscious fears about malicious forces in the darkness.

6. Sleep Hallucinations

Sleep hallucinations refer to the vividly realistic hallucinations that some people experience during the transitional states between wakefulness and sleep. These can occur when falling asleep (hypnagogic hallucinations) or upon waking up (hypnopompic hallucinations).

The hallucinations can involve seeing ghostly apparitions, flashes of light or geometric shapes, or even fully formed images of people, animals, or objects that seem totally real in the moment. Some report hallucinations in other sensory modes like hearing sounds or voices as well.

While they can certainly be disturbing, sleep hallucinations are considered a normal phenomenon caused by a temporary crossing of awareness between dreaming and wakefulness.

As we begin to fall asleep, the brain starts exhibiting neuron firing patterns similar to the REM stage of vivid dreaming. At the same time, the regions for sensory processing remain largely awake and active. This mix of dreaming and waking consciousness allows the vivid dream imagery and scenarios to be perceived as reality.

The reverse transition happens with hypnopompic hallucinations upon waking up. The REM dream state persists momentarily as the sensory areas turn back on, projecting those surreal dreamscapes into the waking experience before fully snapping back to reality.

Sleep hallucinations tend to be more common in those with irregular sleep schedules, excessive daytime sleepiness, sleep paralysis, narcolepsy, or certain psychiatric conditions. Drug use and lack of sleep can also increase their likelihood.

While typically brief and harmless from a physiological standpoint, these hallucinations can understandably be very unnerving and even traumatic if they involve disturbing or paranormal phenomena seeming to intrude on waking reality.

Focusing on establishing optimal sleep habits and sleep environments is recommended for preventing potential disruptive sleep hallucinations. But ultimately, some degree of “waking dreams” is just part of the brain’s natural cycle of cycling between sleep and consciousness for most people.

7. Sleep Head Syndrome

Exploding head syndrome is a distressing and remarkably well-named experience where people hear a tremendously loud noise or explosive crashing sound in their head as they are falling asleep or waking up.

Despite its alarming name, exploding head syndrome is not actually dangerous or indicative of any physical head trauma. The sounds are subjective auditory experiences happening solely within the person’s mind during the transition between wakefulness and sleep.

The noises have been described as incredibly loud explosive blasts, thunderous crashes, loud gunshots, bombshells, or deafening cymbals. Some report the sound having a directionality within their head or seeming to come from an external source at first.

While no definitive cause has been identified, researchers believe exploding head syndrome relates to a type of neurological “glitch” during the changing sleep/wake cycles and consciousness levels. One theory is that it involves firing misfires of the neurons that normally dampen external noises during sleep transitions, causing them to amplify and distort any innocuous real-world sound.

The jarring experience fortunately only lasts a second or two even though it can feel much longer in the stunned aftermath. There are no actual physical explosions or detrimental impacts involved.

However, exploding head syndrome can still be quite traumatic in the moment — abruptly rousing sufferers from sleep in a panic, leaving them worried about their safety and mental well-being. It has been linked to sleep paralysis and hallucinations in some instances as well.

While benign, recurring episodes can start impacting someone’s quality of life through sleep deprivation and anxiety around falling asleep. Reducing overall stress, establishing good sleep habits, and eliminating risk factors like restless leg syndrome may help reduce instances of exploding head syndrome.

and sleep. Researchers believe minor unconscious noises become amplified due to weird neurological firings in this mid-sleep state.

8. Sleep Eating Disorders

Here are more detailed information about the bizarre and unsettling sleep eating disorders:

Sleep eating disorders involve unconsciously getting up in the middle of the night and binge eating unusual foods or even inedible objects — all while in an unconscious sleep-walking state with no memory of the behavior.

The most common of these disorders is the Night Eating Syndrome (NES), where people will actually get up, go to the kitchen, and consume large amounts of food while seemingly awake but completely out of conscious awareness.

Sufferers often report finding evidence of their sleep eating like wrappers, containers, or crumbs and stains around the house the next day. Even more bizarrely, the food items consumed can range from ordinary foods to wildly unappetizing concoctions like raw eggs mixed with ketchup or peanut butter sandwiches covered in toxic substances like household cleaners.

In more extreme cases of Sleep Related Eating Disorder (SRED), people have been known to eat inedible and potentially harmful non-food items like bits of plastic, aluminum cans, cigarette butts, or even pets’ food during these sleep-walking binge episodes.

From a neurological standpoint, sleep eating occurs during a paradoxical overlap of being in a deep sleep state while unconscious eating behaviors controlled by the brain’s wakeful centers are somehow triggered. It remains unclear exactly why some have such episodes.

Sleep eating is more common in females and those with other sleep issues like sleep apnea, restless leg syndrome, or gastric disorders. Potential triggers include excessive stress, sleep deprivation, sedative use, alcoholism, and other psychiatric conditions.

Beyond just the puzzling nature of eating without any awareness, sleep eating poses risks of choking, overconsumption of unhealthy calories, and potential ingestion of toxic substances — making it a legitimate sleep disorder worth treating through counseling, medication, or eliminating causal factors when possible.

While usually non-life-threatening, these unconscious binge eating behaviors at night are undoubtedly disruptive and can even be dangerous, showcasing another unsettling way our unconscious sleeping brains can work against our wakeful interests.

9. REM Sleep Behavior Disorder

REM Sleep Behavior Disorder causes people to physically act out vivid dreams by vocalization, movements and even combative behaviors while they remain unconsciously asleep. It involves a paradoxical mix of being paralyzed by atonic muscle activity yet persisting in vigorous mobility.

Normally during the REM stage of sleep when most vivid dreaming occurs, our brain stems produce a neurotransmitter called glycine that temporarily paralyzes our muscles and limbs. This REM atonia prevents us from acting out the animated adventures unfolding in our dreamscapes.

However, in RBD this paralysis fails to set in properly. The brain’s motor neurons remain enabled, allowing the sleeper’s body to thrash, kick, yell, punch, jump out of bed and overtly “act out” whatever dream narrative is occurring in their mind’s eye.

This dangerous dream-enacting can lead to injurious situations like falling out of bed, punching walls, knocking over furniture and even inadvertently attacking a sleeping partner beside them as they physically confront the dream antagonists.

RBD is classified as a parasomnia and most often found in older males, potentially caused by dysfunction in the brain stem’s sleep/wake and motor regulatory circuits. However, it can strike all demographics to varying degrees.

The disorder has also been linked to neurodegenerative conditions like Parkinson’s, Lewy body dementia, and multiple system atrophy when it emerges without any other identifiable cause in later life. RBD appears to sometimes precede or coincide with development of these neurological diseases.

Given the significant risk of self-harm and harm to others, treatment is vital once RBD manifests — typically through drug therapies to restore muscle paralysis during REM sleep or protective measures like removing hazards and using bed restraints or sleeping separately if severe.

While still poorly understood, this unusual and dangerous parasomnia offers a fascinating case study into the neurology behind REM atonia and the complex interplay between the unconscious dream mind and conscious physicality during sleep.

10. The Corpse

The corpse While seemingly disturbing, research shows most people naturally assume a rigid corpse-like pose during the deepest stages of REM sleep each night. Called the “sleep body position” or “tonic solidity”, the arms and legs fully extend while remaining stiff and utterly still — just like a deceased person. Scientists attribute this phenomena to the total muscle paralysis and lack of movement during this phase of sleep.