Psychiatric Annals

CME Article 

Parasomnias and Criminal Activity

Daniel S. Mundy, MD


Parasomnias are a heterogeneous group of disorders that may result directly in criminal charges. This article provides a general description of these phenomena, the unique forensic aspects of parasomnia defenses, and an overview of accepted and contested approaches in the field of sleep forensic medicine. This article is intended for both general and forensic psychiatrists who might be called upon to provide expert testimony in a crime that originates from a sleep disorder. [Psychiatr Ann. 2017;47(12):588–592.]


Parasomnias are a heterogeneous group of disorders that may result directly in criminal charges. This article provides a general description of these phenomena, the unique forensic aspects of parasomnia defenses, and an overview of accepted and contested approaches in the field of sleep forensic medicine. This article is intended for both general and forensic psychiatrists who might be called upon to provide expert testimony in a crime that originates from a sleep disorder. [Psychiatr Ann. 2017;47(12):588–592.]

This scenario may be familiar: you receive a call from an attorney whose client is charged with committing a violent crime at night, but reports little to no memory of the event. The alleged victim was near the defendant's home, possibly in the home, or even in the same bedroom. The defendant has a prescription for psychotropic medication, and illicit drugs or alcohol may have been involved.

Adult sleep disorders have had a home in psychiatric nomenclature since their inclusion in the Diagnostic and Statistical Manual of Mental Disorders, third edition, revised (DSM-III-R),1 although they are far less frequently invoked in a “not criminally responsible” defense compared to their cognitive, mood, psychotic, intoxicated, and trauma-related kin. This may be due, in part, to the relative infrequency of sleep-related disorders contributing directly to criminal allegations; moreover, in cases of sexual allegations a bed partner may be less inclined to press charges for sexual behavior, possibly contributing to underreporting bias.2 Nevertheless, knowledge of parasomnias and their precipitants is a valuable tool for a forensic psychiatrist.

Noteworthy Cases

A comprehensive summary of cases using sleepwalking defenses is beyond the scope of this article but is available elsewhere.3–5 Only a few noteworthy cases are referenced here.

The first reported sleepwalking defense in the medical literature was published in 1878, when a Scottish man was tried for murder after bludgeoning his 18-month-old child to death against a wall, asserting he dreamed he was protecting his family from a wild beast. He was ultimately acquitted.6

Regina v Parks, a 1989 Canadian case, is a well-cited case of a homicide and an attempted homicide during presumed sleepwalking.7 In brief, a man drove to his in-laws' home, killing his mother-in-law with a tire iron and seriously injuring his father-in-law. Immediately after the attack, he went to a police station and turned himself in. He was initially assessed by a resident physician in psychiatry and tentatively diagnosed with pathological gambling, psychogenic amnesia, and depression.7 At the trial, the defense asserted he was sleepwalking, and ultimately he was acquitted. The case later went before the Supreme Court of Canada, where the defendant's sleepwalking was classified as a “disorder of sleep,” a non-insane automatism, rather than as a “disease of the mind,” a mental disorder met with traditional legal insanity dispositions.7

In a later hearing, the Canadian Supreme Court ruled that the trial court shall decide, on a case-by-case basis, whether the sleepwalking defense should be characterized under the traditional insanity defense.7 Although the United Kingdom has a similar distinction, no case distinguishing between “insane automatism” and “non-insane automatism” has gone before the United States Supreme Court.

In March 2015, a man from North Carolina was tried for murdering his 4-year-old son and attempting to murder his 10-year-old son and 13-year-old daughter in 2010.8 A forensic psychiatrist retained by the defense testified that several factors likely contributed to the violent acts that took place during nonrapid eye movement (NREM) parasomnia. A forensic psychologist retained by the prosecution argued that the defendant had no history of sleepwalking, and that he planned the attacks. The prosecution pointed out that the psychiatrist was not a sleep specialist. The jury had reasonable doubts about the charge of murder, although they asked if they could consider a manslaughter conviction. The Court informed them their only verdicts were “murder” or “not guilty,” and they returned a verdict of the latter.8

Description and Classification of Parasomnias

First Forensic Characterization

In 1974, Bonkalo,9 a forensic psychiatrist, specifically addressed criminal and forensic applications of people charged with crimes immediately after arousal from sleep, specifically, confusional arousals. He identified common features encountered in this group, including a strong childhood and/or family history of sleepwalking, male gender, nocturnal enuresis, nightmares, agitation on awakening, forced arousal from sleep (as opposed to spontaneous awakening), arousal from deep sleep within 30 minutes to 2 hours of sleep onset, arousal from exceptionally deep sleep, apparently unmotivated but seemingly purposeful behavior, a dazed appearance with open eyes, a confusional state of seconds to minutes, and brief amnesia. He also remarked on the role of alcohol and other intoxicants contributing to the deepness of the sleep and predisposing to confusional arousals.

However, Bonkalo9 only dealt with a specific type of sleep disorder (ie, confusional arousal). Parasomnias are, in fact, a heterogenous group of disorders that may all lead to criminal behavior. Therefore, I first begin by presenting their classification.

General Classification

At present, parasomnias are viewed as admixtures of various sleep states and wakefulness.10 The clinical features vary significantly based on the stage of sleep from which the behavior originates; put simply, the differing features reflect partial awakening from either NREM or rapid eye movement (REM) sleep.

NREM Sleep-Related Behavior

NREM sleep arousal disorders (ie, sleepwalking and sleep terrors) result from partial awakening from slow-wave sleep (SWS). Common diagnostic features of NREM parasomnias include little to no dream imagery, amnesia for the episode, and exclusion criteria involving “attribution” to intoxicants and medications.9 Although confusional arousals are not explicitly referenced in the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-5),10 they are viewed as a subset of this disorder and thought to incorporate “sexsomnia,” (ie, sexual behavior during sleep).11 Similar to Bonkalo's observations of confusional arousals,9 sleepwalking episodes typically have the following features: a duration of less than 10 minutes, open eyes with a blank stare, relatively unresponsive to communication, limited recall of the episode, and full cognitive recovery soon after.

Sleep terrors are similar to sleepwalking, only rather than walking, the person typically begins with a panicked scream, frequently sitting up in bed, with accompanying autonomic arousal and behavioral manifestations of fear. The other features are largely the same, including a relative lack of recalled dream imagery outside of brief images.10

Confusional arousals occur in both sleepwalking and non-sleepwalking. They result from a sudden disturbance during SWS. The person awakens in a confusional state that used to be called “sleep drunkenness.” There is disturbance of cognition, emotion, and attention. The person's behavior is confused and may be complex. The episode lasts for a few minutes before both consciousness and clarity return.3,12

The risk of NREM parasomnias is associated with sedative use, sleep deprivation, fatigue, stress, fever, and other sleep-wake disruptions. When occurring during a polysomnography (PSG), the electroencephalogram (EEG) tends to transition from SWS to alpha/theta activity. The disorder tends to present in children, where it is more common in females, and persists through adulthood, at which time when it becomes more common in males. There is a strong familial component.5,9,10,12

REM Sleep-Related Behavior

REM behavior disorder (RBD) is characterized by physical movements paralleling one's physical activity in dream states. Behaviors typically do not occur in the first 90 minutes of sleep and are more common later in the night when REM sleep is more prevalent. The person will have repeated episodes of vocalizations or complex motor behaviors, the eyes remain closed, and they tend to awake without a confusional or disoriented state. People typically have recollection of significant dream material, as opposed to simple imagery seen in sleep terrors. RBD occurs overwhelmingly in men older than age 50 years, and it is notable that 50% of people go on to develop a synucleinopathy (Parkinson's and related disorders). Polysomnography reveals a lack of atonia during REM sleep.9,10,12

Theories of Causation

Relatively recent theories have gained traction in explaining when and how sleep-related behaviors occur, with particular focus on NREM parasomnias. These theories place emphasis on both the brain's demand for SWS, as well as factors that may cause one to be awakened during SWS.

Competing Theories of NREM Sleep-Related Behavior

Predisposition, priming, and precipitating factors. This is a widely held theory with significant evidence supporting it.13–15 Predisposing factors include genetic susceptibility. Priming includes factors that increase SWS or that make arousal from sleep more difficult, such as prior sleep deprivation and situational stress. Precipitating factors include sensory stimuli and sleep-related breathing disorders (eg, obstructive sleep apnea). Some experts believe that sleepwalking is unlikely to occur without one of the three,15 although this has been debated.16

Push/pull theory. A separate push/pull theory does not require the “priming” factor, described above, to increase the depth or amount of SWS.16 In this model, the increased need for SWS (eg, stress or sleep deprivation), combined with factors that tend to decrease SWS (eg, excessive caffeine, or alcohol in some cases), results in an increased likelihood for a vulnerable person to sleepwalk.17,18

The Complicated Role of Alcohol

Alcohol is a particularly difficult player in the diagnosis of parasomnias, even before approaching forensic applications.3,8,16,17,19,20 Alcohol use in people who do not drink regularly prior to sleep tends to reduce sleep onset latency, leading to increased SWS, and more disrupted sleep in the second half of the night. Total REM sleep and REM onset latency tend to be diminished and delayed, respectively, in people who do not drink regularly.21

Despite alcohol having previously been identified as a precipitating factor of confusional arousals and a risk factor for sleepwalking, the role of alcohol in sleepwalking has recently been revised. The International Classification of Sleep Disorders, third edition (ICSD-3)22 highlights the absence of a compelling relationship between alcohol use and a disorder of arousal, stating that, in the presence of alcohol intoxication, disorders of arousals should not be diagnosed. The above position complies with the DSM-5,10 which has removed alcohol from the list of possible triggers for sleepwalking, instead adding a section on the differential diagnosis of alcohol blackout. These major changes have important implications for those forensic cases in which unspecified or excessive amount of alcohol intake is a factor.2

Psychotropic Medications, Causation, and Mimicry

Specific psychotropic medications associated with sleep-related disorders were identified in one study of patients with psychiatric conditions.23 Sedating antidepressants and zolpidem were more commonly associated with sleepwalking. Zolpidem and antidepressants were more common in patients with sleep-related eating disorder, whereas selective serotonin reuptake inhibitors (SSRIs) were more common in patients with RBD.

Sleep-related behaviors after ingestion of zolpidem are particularly well known, although the etiology is not always clear. Zolpidem appears to increase the risk of sleepwalking, despite having similar amnestic and odd behaviors associated with it. Use of zolpidem has been attributed to amnesia prior to, and upon awakening from, sleep.24

Forensic Aspects of Crime Related to Parasomnias

General Guidelines for Forensic Assessment

Although there is not yet a consensus of formal guidelines for the forensic assessment of sleep disorders, there is broad agreement on obtaining the following: a family history, a history of motor activity during sleep as well as amnesia for these episodes, sleep/wake habits including psychotropic substance use, information immediately prior to the forensic event, physical/neurologic/psychiatric evaluations, and video PSG (both at home and in the laboratory).

Scientific Advancements and Lack of Expert Consensus

Cartwright,16 a prominent sleep psychologist, eloquently describes the changing nature of sleep disorders and the courts as follows:

Historically, if the accused had no psychiatric disorder, a positive history of previous sleepwalking episodes, a lack of waking motivation for the attack, and an absence of any memory of what happened, that was usually sufficient for a dismissal of the charges on the grounds that the accused was then in a state of non-conscious somnambulism.

Increased understanding of the effects of psychotropic substances, and of sleep architecture through PSG, results in additional variables that do not make the jury's job any easier.

Debate About the Role of Alcohol

Sleepwalking defenses in the presence of alcohol intoxication are hotly debated,2,4,17,19–21 and Pressman et al.19 present several arguments against alcohol-induced sleepwalking. First, strong opinions are offered on a sleepwalking defense in the context of voluntary intoxication; in general, “claims of alcohol-induced parasomnias presented solely to circumvent the laws of voluntary intoxication should be understood for what they are and rejected.”19 Second, SWS is unlikely to be present at the high levels of alcohol intoxication typically put forth as evidence, as severe intoxication is likely to decrease SWS, whereas increased SWS is theorized as necessary for sleepwalking.19 Third, there is no literature on the effect of alcohol on a known sleepwalker, and much of the current thinking is theoretical.19 Fourth, violence is more likely to occur during intoxication than during sleep.19 Fifth, there is no direct experimental evidence that alcohol predisposes or triggers sleepwalking or related disorders.19

Other experts have argued that alcohol-related sleepwalking should not inherently be excluded as a defense. Substances that may decrease SWS (such as alcohol), when combined with an increased pressure for SWS (such as sleep deprivation), increase the likelihood of sleepwalking episodes.17 Separate experts have raised concerns that defendants are denied a potential valid defense if alcohol use categorically excludes a sleepwalking defense.20

It is potentially helpful for a forensic psychiatrist to be aware of conflicting views in the sleep study field, particularly in regard to alcohol and sleepwalking. One sleep expert and attorney5 references the field focusing on a select group of opinions. He states the latest version of the ICSD-322 demonstrates the dominance of one body of opinion, although there are eminent forensic sleep experts who dissent.5

Medication-Induced Sleepwalking, Lack of Recall, and Voluntary Intoxication

In the case of sedative/hypnotic-induced behaviors, the simplest way to approach the forensic analysis is to regard hypnotic-induced behavior as the result of a drug side effect, thus avoiding labels such as intoxication; if a side effect can wholly explain criminal behavior, then the person would not be criminally responsible.3 This approach, however, does not take into account the defendant's knowledge of that potential side effect, the defendant's previous experience of the side effect, or actions taken by the defendant that might predispose them to that side effect.25,26 As such, sedative/hypnotic-induced sleepwalking can quickly become a complicated defense.

Although a lack of recollection is a common feature in sleepwalking, as well as with medications such as zolpidem, amnesia and unconsciousness are distinctly different entities, complicating zolpidem-related sleepwalking as a defense. Courts tend to presume that people who consume alcohol or illegal drugs should know their potential to induce altered states; in many cases in which zolpidem has been used as a defense, it was taken in combination with alcohol, which the courts tend to view as voluntary intoxication.24

Debate About the Limits of Polysomnography

PSG can be used to demonstrate certain parasomnias, as well as predisposition to parasomnias. However, the methodology of examining data, and the role of using data in asserting a sleepwalking defense, are both debated. For example, the traditional theory that sleepwalking only occurs with increased amounts of SWS has been challenged in more than one high-profile sleepwalking case, and some experts have essentially argued newer methodologies of SWS analysis do not meet the legal standard for admissibility, despite their admission as evidence in the past.17,27–29 Other debated methodologies include stimulating sleepwalking in laboratory settings, using an “alcohol provocation” PSG, and relying on PSGs performed years after the offense.17,28–30

At its simplest, all experts appear to agree that PSG demonstrating a parasomnia, in isolation, is not sufficient for an examiner to conclude that an offense was committed during a parasomnia. Conversely, failure to demonstrate a parasomnia in PSG, in isolation, should not be sufficient for an examiner to conclude an offense was not committed during sleepwalking.


Parasomnias can lead to criminal behavior via a different mechanism than most other psychiatric diagnoses. This is all the more reason for an expert to be aware of their presentation and nuances. Although the field of sleep medicine has diagnostic tools that are downright futuristic when compared to psychiatric clinical diagnosis, the field of sleep forensics is relatively young. Sleep medicine may be experiencing some growing pains as evidenced by some healthy debate regarding the role of the expert witness, although these are reminiscent of forensic psychiatry in the early 1980s that were ultimately fruitful.


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Daniel S. Mundy, MD, is a Clinical Faculty member, Department of Psychiatry, New York University.

Address correspondence to Daniel S. Mundy, MD, 26 Court Street, Suite 2218, Brooklyn, NY 11242; email:

Disclosure: The author has no relevant financial relationships to disclose.


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