Sleep paralysis is a condition characterized by full or semi-conscious waking during sleep, despite an inability to move and/or speak (paralysis). The conscious awareness is thought to be a result of the brain’s inability to properly transition through sleep stages. This leads to abnormal activity of brain waves – with heavy alpha waves, bursts of beta waves, and simultaneous rapid-eye movement (REM activity).
It is the REM activity results in complete muscle “atonia” or an inability to move the body. During this time, a person may be conscious of their body and/or environment, realizing that they’re trapped. To make matters worse, some cases of sleep paralysis may last hours and often include hallucinations. In many cases, the hallucinations are terrifying resembling demons, vicious animals, or evil entities.
Sleep Paralysis Hallucinations: 3 General Types
Research in 1999 by Cheyne, Rueffer and Newby-Clark analyzed cases of 752 sleep paralysis sufferers. These sufferers were asked questions by researchers regarding the symptoms they suffered, when they experienced the attacks, etc. The researchers found that certain sleep paralysis experiences and/or hallucinations differed from others based on specific patterns.
They found that hallucinatory experiences as a result of sleep paralysis could be characterized in one of three groups: “Intruder,” “Incubus,” or “Unusual Bodily Experiences.” They then attempted to hypothesize the neural activation that was responsible for each of these distinct hallucinations.
Intruder Hallucinations (“Sensed Presence”)
The hallucinatory subtype “intruder” refers to sensing the presence of another person and/or entity during sleep paralysis. The intruder subtype is sometimes also referred to as “sensed presence” due to the fact that people feel as if an intruder is present. They may be able to visually (see) and/or auditorily (hear) perceive the intruding presence, but in other cases they may just “sense” an intruder or impending doom.
- Auditory hallucinations: This involves hearing voices, noises, or other odd sounds.
- Sensing another entity: You may sense that another (typically evil) presence is within close proximity.
- Visual hallucinations: Some people claim to have seen an intruder or evil entity during their hallucinatory experience.
What causes “intruder” hallucinations?
Researchers believe that the “intruder” hallucination is a byproduct of the brainstem inducing amygdala activity. The amygdala is the “fear” center of the brain, and when it becomes active, our vigilance increases. During sleep paralysis, it is believed that the amygdala becomes overstimulated and leads to hypervigilance, sensing a potential intruder or presence. The activation of the amygdala has individuals looking for any potential threats or dangers.
- Amygdaloid complex
- Anterior cingulate
Other limbic structures like the amygdaloid complex and the anterior cingulate may play a role in the intruder hallucination during sleep paralysis. It is thought that REM (rapid-eye movement) sleep is capable of triggering activation in these regions. The anterior cingulate has a significant number of connections that extend throughout the cortex.
The amygdaloid complex is capable of producing strong emotions and is involved as an intermediate between strong emotions and our attentional processes. Researchers speculate that a “sensed presence,” particularly one that is threatening, is due to projections from the thalamus to the amygdala. When these projections hit the amygdala, the amygdaloid complex and anterior cingulate become active.
As an individual enters REM stage sleep, microbursts of activation from the brainstem are believed to connect with the thalamus, which is responsible for activating the amygdala and other areas of the cortex. A particular pathway known as the “subcortical thalamoamygdala” serves to alert us in the event of dangers, threats, or emergencies without an in-depth analysis from other regions. It’s a survival feature, and is thought to become activated during these “intruder” hallucinations.
In a standard fear-inducing situation (e.g. walking down a dark alley at night), there is reciprocal communication between brain regions like the amygdala and polymodal association cortex. This allows us to sense danger, but if there’s no real threat upon analysis, our brain tones down activity in the fear-producing regions. In the case of sleep paralysis, a person isn’t able to determine where the “threat” is coming from, and thus isn’t able to turn off the fear response.
This leads to terrifying feelings as a result of the fear-center and fear-pathway activation. Depending on the person, this can be long lasting (minutes) or be relatively quick (seconds). Since the fear-regions are firing in the brain, a person may experience semi-consciousness, leading them to believe it has a source (e.g. sensing an evil presence).
Incubus Hallucinations (“Old Hag”)
The “incubus” subtype of hallucinations during sleep paralysis can be best described as: chest pressure, difficulty breathing, and in some cases, perception of physical pain. This particular subtype of hallucinatory experience is sometimes called the “Old Hag attack.” The name “Old Hag” refers to the thought that an evil witch or “old hag” sits on the chest of victims, making it impossible for them to move.
- Body pressure: Individuals report feeling intense pressure on some part of their body.
- Breathing difficulties: In most cases, people report having a tough time breathing, and usually attribute it to chest or body pressure.
- Chest pressure: The body pressure is most commonly reported as being directly on the center of the chest.
- Pain: Many people perceive pain on the area in which they feel pressure or within surrounding muscle groups.
- Suffocation: It is common to believe that you are being suffocated during an “incubus” hallucination.
- Thoughts of death: People may feel threatened as if they’re going to die as a result of an evil entity such as a witch, demon, or alien.
It should be noted that some of the “incubus” symptoms may occur simultaneously with “intruder” symptoms. However, the predominant characteristics of the “incubus” hallucinations are body pressure (usually on the chest) and difficulty breathing. Secondary characteristics can include: perceived suffocation, thoughts of death (by a threat), and in some cases, evil entities like aliens, demons, ghosts, and witches.
What causes “incubus” hallucinations?
It is hypothesized that various aspects of REM (rapid-eye movement) during sleep are responsible for the symptoms of the “incubus” hallucinations. During REM sleep, our breathing changes, becoming more shallow and rapid. Exact breathing rates during REM can be subject to significant variation, yet it is thought that the perception of “breathing difficulties” is associated directly with REM-induced changes.
The airways can actually become slightly blocked during certain portions of the REM stage. When an individual experiences semi-consciousness as a result of waking during sleep paralysis, they awaken at a time when their body has been rendered immobile and their breathing has become shallow. They believe that since they’re not able to breathe deeply, that they may suffocate – so they attempt to slow their breathing.
When realizing they aren’t able to slow their breathing as a result of REM stage immobilization of muscles, they feel muscular resistance – particularly on the chest. This resistance is interpreted as a heavy pressure on the chest. A person may panic and believe that impending suffocation is likely and will result in death. As they attempt to fight the sleep paralysis, they realize that there’s nothing that can be done.
Due to the fact that their muscles are immobile, they may activate areas in their brain responsible for regulating “struggle.” These areas may lead to the perception of “pain” and/or extremely uncomfortable spasms. Most women perceive this “incubus” form of hallucination as akin to being “raped” or assaulted sexually.
3. Unusual Bodily Experiences (Vestibular-Motor Hallucinations)
Those reporting “unusual bodily experiences” during sleep paralysis may feel as if they are entering another realm of existence. Some people with unusual bodily experiences claim to have had out-of-body experiences (OOBEs), felt as if they were flying, or as if they were floating in space. These can also be described as “vestibular-motor” hallucinations OR hypnagogic/hypnopompic hallucinations.
- Emotional bliss: It is common for those with unusual bodily experiences to report feeling particularly blissful, happy, or content.
- Fictitious motor movements: People may believe that they are moving their body and/or walking around, despite the fact that they’re asleep.
- Floating sensations: Some individuals may feel as if their body is floating in space without being bound to gravity.
- Flying sensations: Others report feeling as if they were flying during their sleep paralysis.
- Inertial forces: People may report a variety of experiences including: falling, lifting, spinning, swirling, accelerating, or decelerating. The most common happen to be flying and floating, but others are documented.
- Lightheadedness: Some people report a significant degree of lightheadedness or dizziness during unusual bodily experiences.
- Out-of-body experiences: It is common for those with recurrent episodes of sleep paralysis to have out-of-body experiences.
- Remote viewing: This is defined as “autoscopy” or the hallucinatory experience of “seeing” yourself from an external, third-person perspective.
Note: Some individuals report being “violently” removed from their bodies during these hallucinations. They describe the experience as being highly forceful. That said, a majority of individuals say that their experience was positive and that they’d repeat it if they were able.
What causes “unusual bodily experiences”?
When you’re awake, various regions of your brain communicate and allow for both head and eye movements. The vestibular system (frontal, temporal, parietal lobes) is a region that is involved in the coordination of these movements, and happens to be closely tied to centers in the brainstem responsible for regulating the sleep-wake cycle. As we enter REM sleep, there are no head movements or images to activate the vestibular region.
The vestibular system connects our body with the external world. Neural firings that stimulate certain regions often result in different perceived “unusual bodily experiences” during sleep.
- Angular gyrus: If this region becomes abnormally stimulated during sleep, we experience out-of-body experiences and/or sensations of floating.
- Parietal lobe: When the parietal lobe is stimulated without movement, we feel as if we’re rolling, falling, or sliding.
These hallucinations are induced as a result of conflicting information about body position, altitude, and motion. Brain scans have revealed that decreases in blood flow to the parietal region can be responsible for many of these unusual bodily hallucinations. The reduced blood flow is a result of poor vestibular integration of motor, tactile, and visual information – resulting in vestibular-motor hallucinations.
- Source: http://www.ncbi.nlm.nih.gov/pubmed/18621363
4. Mixed Hallucinations
Some people experience a combination of sleep paralysis hallucinations, hence being referred to as “mixed hallucinations.” In other words, they may experience the “Intruder” subtype along with “Incubus” – sensing the presence of an evil entity, while simultaneously thinking that the evil entity is putting pressure on their chest in attempt to suffocate them. In other cases, a combination of all three subtypes may occur simultaneously.
In this case, a person may sense an evil presence (Intruder), feel intense pressure on their chest and/or pain (Incubus), and have an out-of-body experience (Unusual Bodily Experience). Researchers have noted that those who are new to experiencing sleep paralysis (novices) tend to note one distinct subtype of hallucination, whereas those who’ve experienced multiple episodes (veterans) generally experience a blending of 2 or 3 hallucinatory subtypes.
Hallucinations: Novice vs. Veteran Sleep Paralysis Sufferers
Oddly enough there are distinct differences between the types of hallucinations experienced during sleep paralysis based on whether someone is new to sleep paralysis episodes (i.e. a novice) or has dealt with recurrent episodes of sleep paralysis for awhile (i.e. a veteran).
- Novices: Those who are novices, or have little experience with sleep paralysis episodes tend to report significantly more “intruder” hallucinations and are unlikely to report any “unusual bodily experiences.” These individuals tend to be of a younger age than the veterans.
- Veterans: Those who are sleep paralysis veterans report significantly more “unusual bodily experiences” and significantly less “intruder” hallucinations. The average age is older than novices, but not significantly. Veterans are more likely to experience “mixed” hallucinations, with 2 to 3 subtypes occurring simultaneously.
Incubus hallucinations: It seems as though the occurrence rates of incubus hallucinations did not significantly differ based on whether someone was new to sleep paralysis or a seasoned veteran. Researchers believe that incubus hallucinations occur with equal likelihood among both novices and veterans.
Unusual bodily experiences: Research from Chayne (2005) discovered that novices to sleep paralysis hallucinations were able to distinguish the “unusual bodily experiences” (vestibular-motor hallucinations) from both “incubus” and “intruder” hallucinations easier than veterans.
Alien abductions (mixed hallucinations): Those considered experienced veterans in sleep paralysis often experience a blending of hallucinations, making them tougher to distinguish. In reports of “alien abductions” during sleep paralysis, all three subtypes of hallucinations are thought to occur – leading to a state of fear, pressure, and unusual sensory experiences.
- Source: http://www.ncbi.nlm.nih.gov/pubmed/10487786
Timing: Beginning vs. End of Sleep Cycle
The timing of when your sleep paralysis episode occurs may dictate the hallucinatory subtype that you experience.
Beginning of cycle: This refers to experiencing sleep paralysis during the transition of wakefulness to sleep, and tends to occur at night (or beginning of the sleep cycle).
- Unusual bodily experiences: Likely
- Incubus hallucinations: Intense
- Fear: Lower levels
End of cycle: This refers to experiencing sleep paralysis during the transition of sleep to wakefulness and tends to occur in the morning (or end of the sleep cycle).
- Intruder hallucinations: Unlikely (Fewer)
- Incubus hallucinations: Reduced intensity
- Fear: Highest levels
Note: Feelings of positive emotion (e.g. bliss) and those reporting sexual experiences didn’t significantly vary based on beginning vs. end of the sleep cycle.
Males vs. Females: Researchers have noted some differences in sleep paralysis hallucinations based on sex. Females reported the highest levels of “fear” associated with their sleep paralysis experiences compared to males. Additionally, females report more intense “incubus” hallucinations in comparison to males.
Have you ever experienced hallucinations during sleep paralysis?
If you’ve experienced an episode of sleep paralysis, did you also experience one of the three hallucinatory subtypes? It should be noted that not everyone will vividly recall whether they experienced a hallucination during sleep paralysis due to the fact that some people are less conscious during REM stage than others. If you have experienced hallucinations during sleep paralysis, feel free to share your experience in the comments section below.