Authors: Vijay Bhalerao, Shashank Gotarkar, Deepak Vishwakarma, Sushim Kanchan
Categories: Neurology, hallucinations, rapid eye movement (rem) sleep, risk factors, sleep paralysis, treatment modalities, Public Health, Epidemiology/Public Health
Source: Cureus
Doi: 10.7759/cureus.65413
Sleep paralysis (SP) is a phenomenon wherein individuals awaken from deep sleep but are unable to move or speak, often experiencing vivid hallucinations. This condition, attributed to the persistence of muscle atonia from rapid eye movement (REM) sleep into wakefulness, is associated with factors like sleep deprivation and irregular sleep patterns. While isolated episodes of SP are generally benign, recurrent episodes may warrant clinical attention, particularly when accompanied by distressing symptoms. Despite its prevalence across cultures and its documented association with various medical conditions, SP remains poorly understood by many. This review explores the clinical characteristics, epidemiology, and associated risk factors of SP, drawing from a comprehensive analysis of the existing literature. Additionally, the review discusses potential treatment modalities, including pharmacological interventions and cognitive-behavioral therapy, highlighting the need for further research to enhance our understanding and management of this intriguing phenomenon.
Keywords: rapid eye movement (rem) sleep, treatment modalities, risk factors, hallucinations, sleep paralysis
Sleep paralysis (SP) is when an individual awakens from a deep sleep yet cannot move or talk. The body is frequently prevented from acting out dreams upon leaving rapid eye movement (REM) sleep, a paradoxical state of sleep in which intense dreams are accompanied by total muscle paralysis. The brain awakens from REM sleep during SP before the body paralysis stops. Being awakened in complete darkness, feeling helpless and paralyzed, and unable to scream are all part of this horrific experience. The sensory flood from the dream world still obscures the person's thoughts, which could lead them to hallucinations. Sleep loss, psychological stress, or irregular sleep cycles can cause this syndrome. The primary symptom is the inability to move or talk upon awakening. Murmurs, voices, roars, and hissing, static, zapping, and buzzing noises are heard. Other signs and symptoms can include a fearful or pushed-down sensation, hypnagogic or hypnopompic experiences, breathing problems, sweating, headaches, muscle aches, or paranoia. SP involves a temporary inability to move or speak upon awakening, often with vivid hallucinations. It occurs when the muscle paralysis typical of REM sleep persists briefly into wakefulness. Factors like sleep deprivation and irregular sleep patterns influence this condition. Recent studies also highlight risk factors such as stress, psychiatric disorders, genetic predispositions, and, notably, hypertension. Despite being relatively common and linked to various medical conditions, SP remains poorly understood [1,2].
SP happens when atonia is based on REM and persists into awakening. Most SP sufferers also have vivid, multisensory, and frequently depressing dream activities during conscious paralysis. For most people, SP is a highly unpleasant experience that may not be readily understood due to the interaction of atonia and waking nightmares. Instead, patients could make sense of it using various non-medical theories. Thus, unexpectedly, SP is assumed to play a role in the development and persistence of many beliefs in the supernatural (e.g., night-time alien sightings and demon attacks) in people with otherwise routine reality tests [3]. More than 75% of SP episodes also include numerous bizarre and often terrifying hallucinations in addition to ongoing muscle atrophy. We can classify these experiences into three groups. Other elements of intruder hallucinations include a strong multisensory visual of an intruder in the bedroom and a feeling of a demonic presence in the space. A pressure-like sensation on the chest, often accompanied by suffocating or choking sensations, is a characteristic of incubus hallucinations. Both of these kinds of hallucinations typically happen simultaneously. False movement sensations, out-of-body experiences, and out-of-body autoscopy are all included in the vestibular-motor (V-M) category of hallucinations [4]. SP in isolation doesn't require regular medical treatment, whereas SP that occurs with narcolepsy does, particularly when symptoms interfere with daily job and home life. The most frequently administered drugs are stimulants and selective serotonin reuptake inhibitors (SSRIs), which help people stay awake and cure narcolepsy. Medical professionals occasionally attach electrodes to the chin, scalp, and outside edges of the eyelids to detect electrical impulses in the brain and brain waves and keep track of breathing and heart rates [1]. This methodological approach provided a structured framework for gathering relevant evidence to address the research questions regarding the relationship between SP, its risk factors, and depression in older adults.
Future research on SP should address both its neurological sequelae and potential improvements in daily routines and treatment approaches. This includes exploring cognitive and structural brain changes, optimizing sleep hygiene, developing personalized treatments, and enhancing public awareness. Understanding these aspects could lead to more effective management strategies and improved quality of life for individuals experiencing SP.
The methodology details the systematic approach employed for a literature review on SP and its correlation with various risk factors. It involved searching three major databases, PubMed, Scopus, and Google Scholar, using Medical Subject Heading (MeSH) phrases such as "Sleep Paralysis," "Rapid Eye Movement (R.E.M.)," "Obstructive sleep apnea," and "Narcolepsy" and Boolean operators "And" to combine terms effectively. The aim was to identify published articles, studies, and research in English related to SP and its associated risk factors. Inclusion criteria were set to include studies published between 1988 and 2024 exclusively focused on depression in older adults and its risk factors. The selection process, depicted in Figure 1, likely involved screening titles, abstracts, and full texts of articles based on predefined criteria. The method used to choose the research is shown in Figure 1 below.
Figure 1 Inclusion and exclusion criteria for the article*Consider, if feasible, reporting the number of records identified from each database or register searched (rather than the total number across all databases/registers).**If automation tools were used, indicate how many records were excluded by a human and how many were excluded by automation tools.
Discussion
SP is when voluntary muscular movements are stopped at the start of sleep or upon waking up. The local surroundings are perceived clearly, and breathing and eye movements are unaffected. These episodes are typically accompanied by a range of hallucinations, including illusory perceptions of movement (V-M hallucinations), pressure on the chest (incubus hallucinations), and a feeling of an evil entity (known as intruder hallucinations). Over 100 different cultures have terminology for SP, making it a truly global occurrence. Experiences with SP are frequently incorporated into a culture. It has been proposed that experiences of SP may be the cause of purported paranormal events like witches [2,5]. A brief partial or total paralysis at the start or end of the sleeping cycle is known as SP [6]. Aside from the limits of the techniques used to detect SP, another significant issue is a lack of consistency in terminology.
Nauseous paralysis during sleep is a typical symptom of narcolepsy. Other symptoms of narcolepsy include daytime tiredness, inconsistent nocturnal sleeping patterns, and cataplexy, which is the spontaneous, brief, bilateral loss of muscle tone in reaction to strong emotions such as laughter or anger [7,8]. In cases where episodes produce clinically substantial fear and distress, some authors sometimes refer to cases as "fearful" isolated SP (ISP). Finally, recurring (frightened) ISP may be used when episodes reoccur. However, no agreement exists about how frequently episodes must occur to be termed recurrent [9].
A recent systematic review of 35 research studies, encompassing a total of 36,533 individuals, found that 7.6% of the population had experienced at least one episode of SP in their lifetime. Students (28.3%) and psychological patients (31.9%) reported higher lifetime incidence percentages of SP, with slightly more women than men reporting it [3,10]. In addition to being associated with conditions such as narcolepsy, hypertension, and seizure disorders, SP episodes have also been linked to shift work, generalized sleep deprivation, airline delays, student status, and African ancestry. When SP occurs in otherwise healthy individuals, it is called ISP. It is no longer recognized that SP and ISP episodes are diagnosable illnesses [2,10]. Numerous studies have demonstrated a connection between poor sleep quality and an increased likelihood of experiencing SP. SP has been associated with symptoms of insomnia, though not with true insomnia. Research also indicates a connection between SP and various strange and frightening sleep experiences, including nightmares, "expanding syndrome," and "lucid dreaming." According to the objective tests, SP is a "mixed" state of consciousness that blends aspects of REM sleep and wakefulness [11].
Risk factors for SP
Several risk factors have been discovered, in addition to the demographic indicators linked to SP that were previously listed. Table 1 lists some medical disorders connected to SP.
SP occurs frequently in the general population and has a unique and dramatic clinical appearance. Many writers, such as Fyodor Dostoevsky, say that SP is characterized by a unique combination of subjective wakefulness and total weakness, distinguishing it from situations where individuals feel sluggish or heavy. During an episode of SP, individuals typically experience a sense of being fully awake but unable to move, which can be extremely frightening, particularly during the first occurrence. This feeling is often accompanied by sensations of pressure on the chest or a heavy weight on the rib cage. These sensations arise because not only are the auxiliary respiratory muscles (intercostal muscles) affected but also the voluntary limb muscles. However, it's important to note that the diaphragm responsible for breathing remains unaffected during SP episodes. This combination of subjective wakefulness, paralysis, and sensations of pressure or weight can contribute to the distressing nature of SP experiences [20,21]. If a person with high blood pressure chose not to go through ISP, they were very likely to have panic episodes often, leading to a diagnosis of panic disorder. This situation was similar to finding out that none of the family members with panic disorder admitted to experiencing ISP [12]. It briefly mentions that people experiencing SP might hear or see voices, leading them to believe they are being attacked. It was reported that the depressing emotions experienced by these patients frequently lingered throughout the next day as acute depression [22]. After reviewing the body of research on lifetime episodes of SP, it was found to be a relatively common occurrence. It is notably more prevalent among students and individuals with mental health conditions, with a minimal discrepancy between these two groups despite occurring in less than 8.0% of the general population. While the reasons behind this higher prevalence remain uncertain, regular sleep issues experienced by both groups likely contribute to the likelihood of experiencing SP episodes [10].
Patients who report experiencing atonic muscles during sleep often overlook this common symptom despite experiencing significant daytime sleepiness that interferes with their daily lives. Polysomnography typically yields unremarkable results, except for scattered nocturnal sleep with decreased REM sleep. Consequently, to confirm a diagnosis of narcolepsy, multiple sleep latency tests (MSLT) are conducted. Subsequently, patients may commence treatment with prescription drugs such as stimulants and antidepressants. For instance, venlafaxine, administered once daily, has been found effective in alleviating cataplexy and SP. However, research investigating the efficacy of specific medications in treating SP is limited [23,24]. Hence, one possible explanation for this correlation could be that individuals experiencing sleep-related auditory or visual hallucinations may interpret them as evidence of the existence of aliens or other supernatural entities. Nevertheless, additional research is necessary to validate this hypothesis and eliminate alternative explanations [25]. The individuals experienced multimodal hallucinations, with many of their encounters aligning with Cheyne-Stokes respirations [26,27].
Alprazolam patients experience improved SP due to its anxiolytic properties, which promote a sense of ease and facilitate a regular, healthy sleep cycle. Similarly, chlordiazepoxide, an anticonvulsant and short-term anxiety medication used to treat alcohol withdrawal symptoms, enhances postural atonia and encourages a regular sleep cycle. The recommendations are based on narcolepsy research, limited case studies, clinical expertise, and logical deductions derived from the key findings on SP and recurrent isolated sleep paralysis (RISP). Fortunately, various practical treatment approaches exist in psychopharmacology and psychotherapy [3]. To prevent and manage SP, individuals should maintain a consistent sleep schedule, aim for 7-9 hours of quality sleep, and manage stress with relaxation techniques. Optimizing the sleep environment by keeping it dark, cool, and quiet, avoiding stimulants like caffeine and alcohol before bed, and sleeping on your side can also help. For ongoing issues, consulting a healthcare professional is recommended. It notes the inclusion of an adherence measure to aid research, although the manual lacks empirical validation. Cognitive-behavioral therapy for ISP involves tailoring sleep hygiene advice to the individual and teaching relaxation methods specifically designed to manage recurring episodes of RISP, in vivo interventions to disrupt episodes, strategies for coping with alarming hallucinations, challenging catastrophic thoughts, and simulating successful resolutions of RISP episodes [28].
Multiple hallucinations are often associated with SP. One component, known as "intruder hallucination," involves feelings of panic, a sense of presence, and both auditory and visual hallucinations. Another component is the incubus hallucination, characterized by chest pressure. Lastly, out-of-body experiences are characterized by V-M hallucinations. ISP is the temporary inability to move from sleep to wakefulness without other clinical signs of narcolepsy. ISP episodes are more commonly linked to hypnagogic events than narcolepsy-associated paralysis, which typically occurs upon awakening from hypnopompic paralysis [29]. During SP, hallucinations occurring during the onset of sleep (hypnagogic) or upon waking (hypnopompic) can manifest in various forms. These include seeing human-like shapes approaching, hearing footsteps, feeling levitation, experiencing autoscopy (out-of-body sensations), or perceiving the presence of a frightening intruder through auditory, tactile, or visual sensations. Specifically, individuals experiencing SP often report hallucinations of a shadowy, human-like figure exerting pressure on their chests as if suffocating them. These universal aspects of the SP experience reported globally across different cultures may stem from underlying neurobiological factors (Hufford, 1982, 1995, 2005). Not surprisingly, SP frequently triggers intense panic and fear in those who experience it [30-32].
Table 2 shows a summary of the study findings included in this review.
During sleep, the body cycles through REM and non-rapid eye movement (NREM) stages. REM sleep involves heightened brain activity, increased heart rate and blood pressure, and faster breathing. Vivid, detailed dreams and occasional nightmares characterize it. Interestingly, REM sleep induces muscular atonia, a temporary paralysis likely to prevent injury from dream-related movements. SP blurs the line between sleeping and waking states. It involves temporary muscle paralysis lasting seconds to minutes, during which individuals are conscious but unable to move. They can breathe, think, and see, yet remain physically immobile. SP may include hallucinations, where individuals perceive unreal alterations in their environment. These can range from simple images to complex sensory experiences like intruder, incubus, or V-M hallucinations [33].
The study's findings indicate that SP occurs when an individual wakes from deep sleep but is temporarily unable to move or speak. This phenomenon is largely attributed to continuous muscle paralysis associated with REM sleep, a phase characterized by vivid dreaming and complete muscle immobilization. Contributing factors include sedentary lifestyles, which are known to exacerbate this condition, and the specific characteristics of an individual's working environment, which can influence both the frequency and severity of SP episodes.