Key Points On Sleep Hallucinations

• Sleep-related hallucinations (SRH) are vivid, dream-like perceptions that occur when falling asleep, during sleep, or upon waking. They are classified as a type of parasomnia, which are undesirable experiences that happen during sleep.

• There are two main types of sleep hallucinations: Hypnagogic and Hypnopompic Hallucinations (HHH), which are very common and often harmless experiences at the edges of sleep, and Complex Nocturnal Visual Hallucinations (CNVH), which are rarer, more disruptive, and more frequently linked to underlying medical conditions.

• While HHH can happen to anyone, they are more common in younger and older individuals and can be associated with other sleep disorders or psychiatric conditions. CNVH are more often seen in older adults with neurologic or visual health problems.

• Diagnosis relies on a patient's description of their experiences, sometimes supported by a polysomnography, which is a type of sleep study. It is important to evaluate them in the context of a person's overall health, as they are often a symptom of another condition rather than a standalone disorder.

An Overview of Sleep-Related Hallucinations

Sleep-related hallucinations are sensory experiences that feel real but are created by the mind. They happen in the transitional states between wakefulness and sleep. These events are officially classified within a group of sleep disorders known as parasomnias.

While the idea of having a hallucination can sound alarming, many of these experiences are quite common and not a cause for concern. They can range from fleeting images or sounds as you doze off to more complex and structured scenes that appear upon waking.

The official classification of sleep disorders recognizes two primary forms of these experiences.

The first and most common type includes hypnagogic hallucinations, which occur as you fall asleep, and hypnopompic hallucinations, which happen as you wake up.

The second, much rarer type is known as complex nocturnal visual hallucinations, which involve waking suddenly during the night to vivid and often startling imagery.

Understanding the differences between these types and their potential links to other health conditions is the first step in managing them.

But what exactly defines these experiences, and how do they differ from dreams?

What Is a Sleep Hallucination?

A sleep-related hallucination is an experience where you see, hear, or feel something that isn't really there. It happens just as you are falling asleep or waking up. According to the International Classification of Sleep Disorders (ICSD-3), these events are typically visual in nature but can involve other senses as well.

Sleep-related hallucinations are considered a formal sleep disorder when they are recurrent and are not better explained by another medical or mental health condition, medication, or substance use (American Academy of Sleep Medicine, 2014; American Academy of Sleep Medicine, 2023).

These experiences fall into two distinct categories:

1. Hypnagogic and Hypnopompic Hallucinations (HHH): These are two sides of the same coin, distinguished only by their timing.

   • Hypnagogic hallucinations happen during the transition from wakefulness to sleep (the "hypnagogic" state).

   • Hypnopompic hallucinations occur during the transition from sleep to wakefulness (the "hypnopompic" state). These are often brief, fragmented, and can feel like an extension of a dream into your waking environment.

2. Complex Nocturnal Visual Hallucinations (CNVH): This is a separate and less common phenomenon. CNVH involves a sudden awakening from sleep during the night, followed by complex and vivid visual hallucinations. Unlike HHH, these episodes interrupt sleep and are often associated with physical actions, like sitting up in bed or pointing at the hallucinated images.

So, just how many people experience these phenomena?

How Common Are Sleep-Related Hallucinations?

Hypnagogic and hypnopompic hallucinations (HHH) are extremely common in the general population, whereas complex nocturnal visual hallucinations (CNVH) are considered rare.

Lifetime prevalence rates for HHH vary widely in studies, ranging from as low as 2% to as high as 75%, though these figures can be influenced by study design (Ohayon, 2000). Research suggests that these experiences are most likely to occur in younger and older people (Ohayon et al., 1996). While they are often harmless, they are reported more frequently by people with certain psychiatric conditions, such as anxiety, PTSD, and mood disorders, where 50% to 80% of people may report them (Ohayon et al., 1996).

In contrast, CNVH have not been studied at the population level. Our understanding of them comes from small case series and reports of patients with existing sleep disorders or other medical conditions (Silber et al., 2005; Takata et al., 1998). They are not considered a common experience among the general public.

This difference in prevalence points to different underlying factors. What are the risks that make these events more likely?

What Causes Sleep-Related Hallucinations? What Are the Risks That Make It More Likely?

The precise causes of sleep-related hallucinations are not fully understood, but they are thought to stem from the brain's complex process of shifting between states of consciousness, such as wakefulness, non-rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep. Sometimes, elements of these states can overlap, leading to unusual sensory experiences.

The risk factors differ between the two main types of SRH:

For Hypnagogic and Hypnopompic Hallucinations (HHH): These are often considered a normal part of the sleep-wake transition. However, certain factors may increase the chances of experiencing or recalling them:

• Age: HHH appear to be more common in younger and older populations (Ohayon et al., 1996).

• Poor Sleep Quality: Frequent awakenings during the night may create more opportunities for these transitional-state experiences to occur and be remembered.

• Psychiatric Conditions: HHH are reported more frequently by people with anxiety disorders, post-traumatic stress disorder (PTSD), and mood disorders (Ohayon et al., 1996).

• Other Sleep Disorders: Conditions like narcolepsy and sleep paralysis are strongly associated with HHH.

For Complex Nocturnal Visual Hallucinations (CNVH): This rarer type is more closely linked to specific health conditions rather than being a normal part of the sleep experience. Key risk factors include:

• Increased Age: The average age of onset for CNVH is around 40 years (Silber et al., 2005).

• Neurologic Conditions: CNVH show similarities to hallucinations seen in disorders affecting the brainstem or visual pathways. These include conditions like Parkinson's disease, Lewy body disease, and others associated with alpha-synucleinopathies, which are a group of neurodegenerative disorders (Manford & Andermann, 1998).

• Visual Disorders: The content of CNVH is sometimes compared to the hallucinations seen in Charles Bonnet syndrome, a condition where people with vision loss experience complex visual hallucinations. This suggests a link to problems in the afferent visual pathway, which is the route that nerve signals travel from the eyes to the brain (Takata et al., 1998).

Given these different risk factors, what do these hallucinations actually look and feel like?

What Are the Signs And Symptoms of Sleep-Related Hallucinations?

The signs and symptoms of sleep-related hallucinations depend entirely on the type being experienced. They can range from simple and fleeting sensations to complex, interactive scenes.

Hypnagogic Hallucinations (As You Fall Asleep) These occur at sleep onset and are often characterized by:

• Primarily Visual Content: This is the most common feature, reported in 55% to 86% of hypnagogic events (Yang et al., 2010; Sidgwick, 1894). The images can be simple, like geometric patterns, shapes, and light flashes, or complex, such as human faces, animals, or entire landscapes (Mavromatis, 1987).

• Multi-Sensory Experiences: Though less common than visual phenomena, auditory sensations like hearing a phone, doorbell, music, or voices occur in 8% to 35% of events (Jones et al., 2010; Hori et al., 1994). Bodily sensations are also frequent, reported in 25% to 50% of cases, and can include feelings of being touched, bodily distortions, or a sense of flying or falling (Foulkes & Vogel, 1965; Ohayon, 2000).

• Low Emotional Impact: Emotional content, such as fear, is rare, occurring in less than 5% of these experiences (Ohayon et al., 1996).

• Brief and Fragmentary Recall: If a person is awoken during the experience, they may recall it, but the memory often fades quickly.

Hypnopompic Hallucinations (As You Wake Up) These occur upon awakening and often feel like a dream is spilling over into reality. Key features include:

• Continuation of a Dream: They often feel like a direct continuation of a dream sequence. A person you were just dreaming about may appear to be in your bedroom after you open your eyes (Takata et al., 1998).

• Vivid and Intense Imagery: The experiences are described as vividly real.

• Uncertainty: Individuals are often unsure whether they are awake or still dreaming.

• Better Memory: Forgetting seems to be less rapid than with hypnagogic hallucinations, and the memory can linger after awakening.

Complex Nocturnal Visual Hallucinations (CNVH) These are distinct from HHH and are more disruptive. Their characteristics include:

• Sudden Nighttime Awakening: The episode begins with a sudden arousal from sleep, typically NREM (non-rapid eye movement) sleep.

• Complex Visual Content: The hallucinations involve complex images like small animals (insects, rodents), people, or distorted forms. These images may be superimposed onto the real environment (Takata et al., 1998; Silber et al., 2005).

• Behavioral Acting Out: The person is not passive. They may sit up in bed, look around, point at non-existent objects, or mumble unintelligibly. Their eyes are often open and may track the hallucinated objects (Gnoni et al., 2022; Castelnovo et al., 2021).

• Emotional Response: Unlike many HHH experiences, CNVH can cause significant fright, alarm, or other emotional reactions.

• Clear Recall: The person typically has a good recollection of the vivid, dream-like imagery after the episode ends.

So, with such a wide range of experiences, how does a doctor figure out what's happening?

How is a Sleep-Related Hallucination Diagnosed?

A diagnosis of a sleep-related hallucination is primarily based on a person's detailed description of their experiences, combined with a thorough medical history. In some cases, objective sleep studies may be used to rule out other conditions and understand the context in which the hallucinations occur.

The diagnostic process typically involves:

1. Subjective Reports: The most important part of the diagnosis is your own description of what happens. A doctor will ask questions about what you experience, when it happens (falling asleep, waking up, or in the middle of the night), what the content is like, how it makes you feel, and whether you do anything physically during the episode. This can be done through clinical interviews or structured surveys.

2. Objective Sleep Studies: To get a clearer picture of brain activity during these events, a doctor may recommend a polysomnography. This is an overnight sleep study that records brain waves (using an electroencephalogram, or EEG), eye movements, muscle activity, heart rate, and breathing. This can help identify the specific sleep stage the hallucinations are emerging from and can be very important for diagnosing associated conditions like REM sleep behavior disorder or narcolepsy. For example, studies have shown that CNVH can arise from NREM sleep and are associated with a distinct EEG pattern of low-voltage, mixed-frequency signals (Gnoni et al., 2022).

It is important to note that recalling events that happen in a different state of consciousness can be difficult. Memory can be affected by the time that has passed since waking and the natural amnesia that occurs when we fall asleep (Wyatt et al., 1994). A doctor will take these factors into account when making a diagnosis.

Are these hallucinations a standalone issue, or are they connected to other health problems?

Health Problems Linked to Sleep-Related Hallucinations

Sleep-related hallucinations are often not an isolated issue; they are frequently a symptom or feature of another underlying sleep disorder, medical condition, or psychiatric disorder.

Sleep Disorders:

• Narcolepsy: HHH are a classic symptom of narcolepsy, a neurological disorder characterized by overwhelming daytime sleepiness. Between 33% and 80% of individuals with narcolepsy experience them (Sz}ucs et al., 2003).

• Sleep Paralysis: This condition involves a temporary inability to move or speak while falling asleep or waking up. It is often accompanied by frightening hallucinations, such as feeling a presence in the room or a weight on one's chest (the "incubus phenomenon"). These hallucinations can be auditory, visual, and tactile (Cheyne et al., 1999).

• REM Sleep Behavior Disorder (RBD): In RBD, a person acts out their dreams. While the main feature is physical action, the underlying dream content that is acted out is a form of sleep-related perceptual experience.

• Nightmare Disorder: Nightmares share features with SRH, particularly the frightening content. However, upon waking from a nightmare, a person is usually fully aware of who and where they are, which is not always the case with CNVH (American Academy of Sleep Medicine, 2014).

• Sleep Terrors: These episodes involve sudden arousal from deep NREM sleep with intense fear, screaming, and confusion. While memory of the event is often poor, fragments of terrifying dream-like images or hallucinations are sometimes reported.

Neurologic and Medical Conditions:

• Neurodegenerative Disorders: CNVH, in particular, are associated with conditions like Parkinson's disease and Lewy body disease. The visual hallucinations in these disorders share many features with CNVH, suggesting a common underlying issue in the brain's visual processing systems (Barnes & David, 2001).

• Brainstem Lesions: A condition known as peduncular hallucinosis, caused by damage to the brainstem, can produce complex, vivid, and colorful visual hallucinations that resemble CNVH (Benke, 2006).

• Visual Disorders: Conditions that impair vision can lead to complex visual hallucinations, as seen in Charles Bonnet syndrome. The similarity in the content of these hallucinations and CNVH suggests a shared mechanism related to the visual cortex generating its own images in the absence of normal sensory input (Takata et al., 1998).

Psychiatric Conditions:

• HHH are reported more frequently in people with anxiety disorders, PTSD, mood disorders, and psychotic disorders (Ohayon et al., 1996). It is thought that poor sleep quality and frequent awakenings common in these conditions may contribute to a higher recall of these experiences.

How do these varied experiences impact a person's day-to-day life?

How Sleep-Related Hallucinations Affects Daily Life

Information on the specific day-to-day impact of sleep-related hallucinations is not detailed in the provided source material. However, based on the descriptions of the experiences, we can infer some potential effects.

For many people, hypnagogic and hypnopompic hallucinations are benign, fleeting, and may even go unnoticed. They are often considered a normal experience and not a sign of a medical problem. However, when the content is frightening, such as in the case of "Terrifying Hypnagogic Hallucinations" or some episodes of sleep paralysis, it can cause a profound sense of fear or dread. This could lead to anxiety around bedtime and a reluctance to fall asleep.

Complex nocturnal visual hallucinations (CNVH) are more likely to be disruptive. Because they involve a sudden awakening and are often accompanied by fear or alarm, they can significantly disturb sleep. The associated behaviors, like sitting up or calling out, could also be concerning for a bed partner. The distress from these episodes may contribute to poor sleep quality and next-day fatigue.

Given these potential effects, what can be done to manage them?

How Are Sleep-Related Hallucinations Treated?

There is no current recommended treatment for sleep hallucinations. Where hallucinations are symptoms of another sleep disorder, treatment focuses on addressing the identified underlying cause, such as narcolepsy, another parasomnia, or a medical condition.

What can a person do to cope with these experiences?

Tips for Living Well With Sleep-Related Hallucinations

While specific medical treatments are not established, several points can help you understand and manage these experiences:

• Recognize Normalcy: Understand that infrequent hypnagogic or hypnopompic hallucinations are very common and may fall within the limits of a normal sleep-wake transition. Not every strange sensory experience around sleep requires intervention.

• Look for Patterns: Pay attention to other symptoms that occur alongside the hallucinations. The presence of daytime sleepiness, acting out dreams, or episodes of sleep paralysis can be important clues that point to an underlying sleep disorder that needs to be addressed.

• Improve Your Sleep Environment: For CNVH, hallucinations may disappear when the room is made brighter (Silber et al., 2005). Keeping a dim nightlight on or having a lamp that is easy to turn on may help end a frightening episode more quickly.

• Focus on Overall Sleep Health: Since poor sleep and frequent awakenings can increase the opportunity for HHH, focusing on good sleep hygiene, maintaining a regular sleep schedule, creating a relaxing bedtime routine, and ensuring your bedroom is dark, quiet, and cool, may be beneficial.

At what point should these experiences prompt a visit to a healthcare professional?

When to Get Professional Help for Sleep-Related Hallucinations

You should consider seeking professional help if your sleep-related hallucinations have any of the following characteristics:

• They are recurrent and frequent.

• They cause you significant distress, fear, or anxiety.

• They disrupt your sleep or the sleep of your bed partner.

• They are accompanied by other concerning symptoms, such as:

  • Excessive daytime sleepiness (a potential sign of narcolepsy).

  • Acting out dreams physically, which could be dangerous (a sign of REM sleep behavior disorder).

  • Episodes of being unable to move when falling asleep or waking up (sleep paralysis).

  • Other unusual nighttime behaviors like sleepwalking or screaming.

A healthcare provider, particularly a sleep specialist, can conduct a thorough evaluation to determine if the hallucinations are a benign occurrence or a symptom of a condition that requires treatment.

Key Takeaways About Sleep-Related Hallucinations

• Sleep-related hallucinations are a type of parasomnia involving sensory experiences around sleep.

• The most common forms, hypnagogic (sleep onset) and hypnopompic (waking) hallucinations, are widespread in the general population and are usually harmless.

• A rarer form, complex nocturnal visual hallucinations (CNVH), occurs upon waking in the night, is more disruptive, and is more strongly associated with underlying neurologic or visual conditions.

• These experiences are not always a sign of a disorder, but when they are recurrent, distressing, or occur with other symptoms like daytime sleepiness or acting out dreams, they warrant a medical evaluation.

• Diagnosis is based on your description of the events, and a sleep study may be used to identify or rule out other sleep disorders.

Frequently Asked Questions About Sleep Hallucinations

Q1: What are the main types of sleep-related hallucinations?

A1: There are two main types of sleep-related hallucinations recognized by the International Classification of Sleep Disorders. The first and most common type is Hypnagogic and Hypnopompic Hallucinations (HHH), which are sensory experiences that happen as you fall asleep (hypnagogic) or wake up (hypnopompic). The second, much rarer type is Complex Nocturnal Visual Hallucinations (CNVH), which involve suddenly waking during the night to vivid and complex images, often accompanied by physical actions like sitting up in bed (American Academy of Sleep Medicine, 2014).

Q2: What is the difference between a sleep hallucination and a dream?

A2: The line between a sleep hallucination and a dream can sometimes be unclear, especially for experiences at sleep onset. However, a key difference is that hypnopompic hallucinations (upon waking) and Complex Nocturnal Visual Hallucinations (CNVH) often continue even after your eyes are open, making them feel as if they are part of your real environment. In contrast, when you wake up from a typical dream, you usually recognize that the experience was not real and was confined to your mind.

Q3: Are sleep hallucinations a sign of mental illness?

A3: Not necessarily. Hypnagogic and hypnopompic hallucinations are very common and often harmless experiences in the general population. However, they are reported more frequently by people with certain psychiatric conditions, such as anxiety disorders, PTSD, and mood disorders, where prevalence can be between 50% and 80% (Ohayon et al., 1996). Therefore, a thorough clinical assessment will consider them as part of a person's overall health profile.

Q4: What causes sleep-related hallucinations?

A4: The exact causes are not fully known, but they are thought to happen when the brain's states of wakefulness, NREM sleep, and REM sleep overlap or transition improperly. Risk factors for the common hypnagogic and hypnopompic hallucinations include being younger or older, poor sleep quality, and other sleep disorders like narcolepsy (Ohayon et al., 1996). The rarer Complex Nocturnal Visual Hallucinations (CNVH) type is more closely linked to underlying health issues, such as neurologic conditions like Parkinson's disease, visual disorders, or lesions on the brainstem (Manford & Andermann, 1998; Benke, 2006).

Q5: Can sleep hallucinations involve sounds or feelings?

A5: Yes. While they are most often visual, sleep-related hallucinations can involve multiple senses. Auditory experiences, such as hearing voices, music, or a doorbell, are reported in 8% to 35% of hypnagogic events (Jones et al., 2010; Hori et al., 1994). Bodily sensations are also common, occurring in 25% to 50% of reports, and can include feeling a touch, a sense of bodily distortion, or the feeling of flying or falling (Foulkes & Vogel, 1965; Ohayon, 2000).

Q6: Is it normal to see geometric patterns or shapes when falling asleep?

A6: Yes, this is a very common feature of hypnagogic hallucinations. Visual images at sleep onset can range from simple, kaleidoscopically changing phenomena like geometric patterns, shapes, and flashes of light to more complex scenes involving people or animals (Mavromatis, 1987). These simple visual experiences are considered a normal part of the transition into sleep for many people.

Q7: When should I see a doctor for sleep hallucinations?

A7: You should consider getting professional help if your sleep-related hallucinations are frequent, cause you significant fear or distress, or disrupt your sleep. It is especially important to see a doctor if they occur alongside other symptoms like overwhelming daytime sleepiness, physically acting out your dreams, or experiencing episodes of being unable to move (sleep paralysis), as these can be signs of an underlying sleep disorder that needs treatment.

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Written By: Dan Ford, DBSM, Sleep Psychologist

Published By: The Better Sleep Clinic Team