Although it is not clear exactly how many people experience parasomnias, or sleep disorders, it is likely that you — or someone you know — have faced at least one such event at some point.
Parasomnias are often associated with unsettling actions or behaviors, made all the more strange for being acted out in a person's sleep, while they are completely unconscious.
However, although some of the strange things that we do in our sleep may be connected with the presence of a sleep disorder, others are, in fact, normal physiological occurrences that are extremely common.
In this Spotlight, we look at five of the strangest things some people do while they're fast asleep.
1. Sleep talking
Sleep talking, or somniloquy, is a common physiological phenomenon, and it is reportedly more frequent in children and adolescents, though it is not an unusual occurrence in adults.
As Shelly Weiss notes in the book Parasomnias, episodes of sleep talking don't tend to last very long, and they don't, in fact, always include intelligible speech.
"Sleep talking is usually brief and infrequent, but can range from a person making a few sounds during sleep that are brief and unintelligible, to full phrases with understandable content or even frequent and long speeches which sound hostile or angry."
A recent study conducted by Dr. Isabelle Arnulf of the Pitié-Salpêtrière Hospital in Paris, France, investigated what sleep talkers are likely to say, and found that, in 10 percent of cases, sleep speech is rich in swear words and negative content.
In fact, swear words featured 800 times more often during sleep discourse than they normally did in an individual's daytime talk.
Dr. Arnulf notes that this may be because sleep talking likely occurs in response to a negative dream situation that makes such impulsive and unguarded speech excusable.
Weiss explains that sleep talking episodes can occur at any stage of sleep and that they are "only disturbing to others," that is, to bed partners.
And I can confirm — my partner's sleep talking episodes, in which he usually expresses distress, never fail to unsettle me. But since he never remembers these occurrences the morning after, they don't bother him at all.
But there are, according to Weiss, external situations that "may precipitate" sleep talking, so if you know that you — or your loved one — are prone to this, then eliminating these factors may help.
They include feverishness due to illness, experiencing stress and anxiety during day-to-day life, lack of sleep, or living with a sleep disorder.
Sleepwalking, or somnambulism, is perhaps the best-known type of parasomnia, having captured people's imaginations for years, and featuring prominently in literature and movies.
This sleep disorder usually takes place during the stage three non-rapid eye movement (NREM) sleep; this is a "deep sleep" period in which brainwaves slow down, and breathing also becomes deep and slow-paced.
People cannot be easily woken at this stage, which is partly what makes sleepwalking so unsettling, as the somnambulist is physically active while still emerged in a deep state of slumber.
But the weirdness does not stop here.
Specialists Frank Ralls and Madeleine Grigg-Damberger write in Parasomnias that sleepwalkers may appear concomitantly awake and "not there" to anyone witnessing their actions:
"[Sleepwalking] episodes often begin with the individual sitting up in bed, fumbling with bedclothes, looking about in a confused manner before getting out of bed and slowly beginning to walk around. The eyes are usually open, often wide open with a confused 'glassy' stare..."
Frank Ralls, Madeleine Grigg-Damberger
They also add that "[t]he person often walks toward sound, light, or a particular room," and they may engage in complex behaviors, such as changing clothes, opening doors, or using the bathroom.
A related sleepwalking disorder is that of sleep-related eating, in which individuals get out of bed, make their way to the fridge, and have a snack, all without actually waking up.
The eating behavior is usually compulsive, and the person could wake up the next morning to find a mountain of incriminating — and shocking — evidence, in the form of dirty wrappers and food containers, as in this case study.
There are, however, some sleepwalking behaviors that are much more dangerous than overeating. One such example is that of sleep driving, in which a person drives a motorized vehicle technically on autopilot, while fully unconscious of their actions.
Some scientists blame these episodes on a short-circuitry caused by certain sleeping aids, the so-called "z-drugs" — zolpidem and zopiclone — though it is not entirely clear to what extent these are at fault.
Though no scientific studies have yet been conducted to address this issue, apparently sleep texting is not uncommon, especially among adolescents.
Over the past few years, various media outlets have reported cases of teenagers embarrassed to find out they had sent text messages to their friends or their crushes while asleep.
One young woman told The Atlantic that she woke up one morning to find that she had made plans to see her ex-boyfriend, which she didn't remember and immediately regretted.
Sleep specialists have declared that this is a new feature in terms of sleep disorders, and the behavior is not yet listed in specialized textbooks.
The specialists blame it largely on the fact that many teenagers have poor sleep hygiene, having become glued to their smartphones, texting away late into the night, and allowing notifications to disturb their slumber.
3. Sleep starts
Many of you are probably familiar with the phenomenon of sleep starts, or "hypnic jerks."
These are characterized by a sensation of falling from a great height, or tripping, which causes the body to jerk and the sleeper to wake up — literally "with a start."
Weiss notes that sleep starts "frequently occur in normal people and at any age," with a prevalence of approximately 60–70 percent in adults; they are not considered a type of sleep disorder.
Typically, the muscle contractions last for less than 1 second, and they occur as a person is about to transition to a state of sleep, or during a stage of light sleep.
Some less common accompanying sensations listed by Weiss include "an auditory sound such as an utterance," and the terrifying perception of a "loud bang or flash of light," also known as "exploding head syndrome."
Although sleep starts are a normal occurrence, scientists suggest that certain factors may increase their likelihood. According to Weiss, these include, "fatigue, emotional stress, sleep deprivation, vigorous exercise, and stimulants such as caffeine and nicotine."
4. Sexual acts
Some of the most controversial unconscious acts performed during sleep are those of a sexual nature, especially when the individual attempts to involve an unwitting co-sleeper.
These acts are characteristic of a parasomnia known as "sexsomnia," in which individuals "display sexual vocalizations, masturbation, fondling, or intercourse/attempted intercourse during sleep — followed by morning amnesia."
Similarly to sleepwalking, sexsomnia takes place during the NREM stages of sleep, and, according to a case report published last month, "only 95 clinical cases" have been documented until now. The report authors also add that most of these cases feature male sleepers.
In some cases, sexsomnia is just an embarrassing occurrence, but in other, more extreme examples, the sleepers can end up sexually assaulting a sleeping partner.
But due to the fact that they remain unconscious throughout these acts, and they cannot remember them the following morning, violent sexual acts committed during sleep remain deeply challenging when brought to court.
The authors of one case report note that, in the instance that they evaluated, the patient affected by sexsomnia managed to gain some control over these night-time occurrences by attending psychotherapy sessions targeting stress management.
5. Acting out dreams
Finally, the parasomnia known as rapid eye movement (REM) sleep behavior disorder is, much like sleepwalking, characterized by the performance of fairly complex actions while in a state of sleep.
However, there are also several differences between the two sleep disorders.
As its name suggests, REM sleep behavior disorder takes place during the REM stage of sleep, when most of the dreaming happens.
Individuals with this behavior disorder tend to "act out" or physically respond to whatever takes place in their dreams, which isn't always great news.
As Sujay Kansagra and Bradley Vaughn write in Parasomnias, "Dream content is [...] reported to become more violent with [REM sleep behavior disorder] onset, and involves the subject being attacked or having to defend a position or others."
Kansagra and Vaughn also note that most individuals with this disorder are over 50 years of age, though its incidence and prevalence rates are unclear.
Such troubled sleepers may make chaotic movements that correspond to their dream content, but fortunately, they are not usually physically violent, either toward themselves or others.
However, violent behavior is more often present in men than it is in women with REM sleep behavior disorder.
Moreover, Kansagra and Vaughn point out that more than 50 percent of individuals with narcolepsy — another sleep-related disorder — also report the symptoms of REM sleep behavior disorder.
If you or someone you know live with a sleep disorder and would like to learn more about it and how to manage it, you may find it useful to access the webpages on "sleep and sleep disorders" curated by the Centers for Disease Control and Prevention (CDC).