What Causes Sleep Violence?

Over the years, I’ve treated a number of patients with violent and dangerous parasomnias. In all of these cases, the stakes are especially high. Not only is my patient’s sleep and health compromised, but their safety—and the safety of other people, especially those closest to them—is very much at risk.

Sleep forensics is a branch of sleep medicine that investigates and seeks to understand violent, strange, and irrational behavior related to sleep. These investigations are necessary when sleep issues may be related to crimes. But sleep forensics also helps us better understand the phenomenon of sleep violence, even when the behavior isn’t criminal.

I think it’s important to understand that sleep violence exists and how it can occur. Incidents of sleep violence happen more often than many people realize. Violence during sleep isn’t common, but it’s also not extremely rare. Estimates indicate that approximately 1.7 to 2 percent of the population experience some form of sleep-related violent behavior.

What causes sleep violence?

Several factors in a person’s life can elevate their risks for sleep-related violence. These include:

• History of parasomnia (sleepwalking, sleep talking, etc.)
• Stress and psychological conditions
• Alcohol and drug use (especially within a few hours of bed)
• Medication interactions
• Lack of sleep
• Physical and mental health conditions, including epilepsy, a neurodegenerative disease, such as Parkinson’s and some forms of dementia, and dissociative disorders, such as PTSD

Often, it’s a cluster of these risk factors together that creates the conditions for sleep violence in a person’s life.

The Sleeping Mind Is an Active Mind.

It’s easy to think of sleep as a time when the “off” switch has been flipped in the brain. Without waking consciousness and memory, the hours you spend sleeping can seem like lost time. But in truth, the brain and body are active throughout every stage of sleep—growing and repairing cells and tissues, rebooting the immune and metabolic systems, restoring organ function, and processing memory, emotion, and recent learning.

Sleep isn’t a void of consciousness. Rather, it involves a different form of consciousness—or being—with different brain activity (I’m talking about dreams here). The main states of sleep consciousness are REM sleep and non-REM, or NREM, sleep. Each has patterns of brain activity that are distinct from one another and distinct from waking consciousness. (This is how we classify sleep stages, based on the different brain waves.)

Many parasomnias, including those which can put a sleeper at risk for sleep-related violence, occur as a person moves between NREM, REM, and wakefulness.

Patients and families who are coping with violent and disruptive sleep behaviors ask me: How is it possible for a sleeper to act out so intensely while still asleep? Understanding sleep as an active state of being, rather than a pause button, is one important step in understanding how these behaviors can come about.

How Sleep Works in the Brain

The next step is to grasp what scientists are increasingly recognizing themselves: Sleep is a local, rather than a global, condition in the brain. What do I mean by that? No single state—REM, NREM, or waking—takes over the brain exclusively. It’s possible for these different states to overlap and occur simultaneously. Especially during transitions among the different states, characteristics of both sleeping and waking can be present in the brain. I think of the brain, when it comes to sleep, like a hybrid car: Sometimes it uses gas, and sometimes it uses electricity.

Here’s an example of what I mean, using a parasomnia known as sleep paralysis. When you experience sleep paralysis, you wake up from sleep and cannot move or speak. It’s a frightening and disorienting episode that can last for a few seconds, and even up to a few minutes. In a state of sleep paralysis, you’re actually in a combination of waking consciousness and REM sleep. REM includes a temporary paralysis of major muscle groups, known as REM atonia, which is thought to keep you immobilized during an active dreaming stage. People who experience sleep paralysis wake with aspects of REM sleep still active in the brain.

When different characteristics of different states of consciousness occur in the brain at once, it creates the terrain for unusual, odd, disruptive, and even violent behavior to occur.

Causes of Sleep Violence

Let’s take a closer look at some of the conditions that are associated with sleep violence.

Sleepwalking and other arousal disorders. Some of the most well-known cases of sleep-related criminal violence have involved the so-called “sleepwalking defense.”

Sleepwalking is considered a NREM parasomnia, meaning it typically occurs during the deeper stages of NREM sleep. There’s a broad range of behaviors that can take place in a sleepwalking episode, ranging from wandering around the bedroom to having conversations, driving, and executing other complex tasks—all while still in a state of sleep.

More than 3 percent of the adult population may experience sleepwalking—and sleepwalking appears to be becoming more common, according to scientists. There’s a strong genetic component to sleepwalking—it tends to run in families. If you were a sleepwalker as a child, you may also be one as an adult, provided the right conditions.

Stress is one factor that may trigger and escalate sleepwalking behaviors. So, too, can sleep deprivation. In several high-profile criminal cases, sleep experts have cited stress and lack of sleep as contributing factors to violent behavior during sleepwalking. That was true in the Kenneth Parks case, one of the most well-publicized cases of sleep violence in recent times. Stress and sleep deprivation also played a role in the case of Joseph Mitchell, who in 2015 was acquitted of murder and attempted murder. The defense said Mitchell was sleepwalking during an attack in which he smothered his 4-year-old son and attacked two other children. Mitchell has also been under acute stress and had suffered from a significant lack of sleep prior to the attack.

Sleepwalking is a type of parasomnia known as an arousal disorder. Arousal disorders tend to arise from non-REM (NREM) sleep. They also often first present themselves during childhood and will frequently diminish or disappear with age. Arousal disorders typically share some common characteristics, including:

• An absence of memory
• Slowed, slurred, or strange speech
• Mechanical answers to questions
• An appearance of confusion, or just staring off

In addition to sleepwalking, other sleep-related arousal disorders linked to violence include:

Confusional arousals. This form of parasomnia is sometimes referred to as “sleep drunkenness.” During a confusional arousal, the sleeper “wakes” into a disoriented state, and may exhibit strange behavior that they’ll have no memory of later. In 1960, American Army Sergeant Willis Boshears was acquitted in England of the murder of a young woman, Jean Constable, after claiming he’d been in a state of sleep confusion during the attack.

Sleep terrors. In one of the cases I've discussed previously, Brian Thomas killed his wife while acting out in response to what appeared to be a sleep terror. Sleep terrors are intensely frightening episodes during which a sleeper often screams and sometimes physically lashes out. In Thomas’s case, he said he believed he was attacking an intruder during what was actually the attack on his wife. Sleep terrors can put the sleeper and others at risk for accident, injury, and assault.

In some cases, fatal reactions to sleep terrors or other arousal disorder parasomnias might at times be mistaken for suicide. The death of artist and designer Tobias Wong has been pointed to as a possible “pseudo-suicide.” Wong, who died in 2010, had a long history of sleepwalking and sleep terrors. His family and friends believe he hanged himself while in a sleep state, unaware of what he was doing.

Sexomnia. This NREM parasomnia involves a person engaging in sexual behavior while in a sleep state. As with other arousal disorders, the person often has little to no memory of their actions. Sexomnia can result in instances of sexual assault, rape, and other sex-related crimes.

Like sleepwalking, other arousal disorders may be triggered or exacerbated by additional factors, including:

• Drug and alcohol use
• Medication, including sleep medications
• Lack of sleep
• Stress and emotional upheaval

REM sleep behavior disorder (RBD). This highly disruptive, potentially dangerous parasomnia occurs during REM sleep, rather than NREM. In normal REM sleep, the body becomes largely immobilized — that’s the temporary paralysis known as REM atonia. REM is a state of active and vivid dreaming, and this temporary paralysis protects the sleeper against acting out in response to dreams.

In people with RBD, there is no REM atonia, no paralysis to keep you from acting out physically while you dream. Sleepers with RBD often react violently, screaming, thrashing, jumping around, kicking, and punching in reaction to disturbing dreams. Injury is an all-too-common consequence of RBD. Research indicates that nearly one-third of those with REM sleep behavior disorder have injured themselves—and 64 percent have injured their sleeping partners—during an episode.

This sleep disorder is linked to:

• Neurodegenerative diseases, including Parkinson’s disease (RBD sometimes occurs as a precursor to Parkinson’s disease, but not everyone with RBD will develop a neurological disease)
• Alcohol, drug, and medication withdrawal, including withdrawal from sedative-hypnotics and antidepressant medications

In roughly half of the cases of RBD, the underlying cause is not known.

Sleep deprivation. It’s important not to overlook the risks that can arise from lack of sleep. Sleep deprivation compromises reaction time, reduces focus and attention, and interferes with good judgment. Insufficient sleep makes us more emotionally reactive and more inclined to engage in risky behavior. The hazards of sleep deprivation are widespread and can result in behavior that’s both dangerous and criminal in nature:

Accidents at home and in the workplace are significantly more likely. According to research, at least 13 percent of workplace accidents are connected to sleep problems. And sleepy workers are 70 percent more likely to have an accident at work than non-sleepy workers.

Sleep and fatigue are common causes of motor vehicle accidents. Drowsy driving is as dangerous as drunk driving to your safety and the safety of others. At least 100,000 motor vehicle crashes are attributable to sleep and fatigue, according to the National Transportation Safety Board. And that’s a conservative estimate, based on accidents reported to police.

Sleep deprivation is a public safety hazard. Low on sleep, public transportation and public safety workers—from train operators to airline pilots, law enforcement personnel to health care workers—are at increased risk for errors and accidents that put themselves and the public at risk. Sleep deprivation has also been a factor in large-scale environmental health disasters, including Three-Mile Island, Chernobyl, and the Exxon Valdez oil spill.

Sleep forensics explores areas of sleep phenomena that remain too-little understood. That work can help move our legal system to better address sleep-related violence, and help keep us all safer by better understanding our capacity for dangerous behavior even during sleep. I want sleep to be a peaceful experience for you and for all my patients. But as with so much about sleep, it’s not that simple.