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Unwanted Bedfellows: The Science Behind Sleep Paralysis Demons

By Brittany McVicar

You jolt awake. You are gasping for air, but you cannot take a breath. As you look towards the foot of your bed you see a dark figure hunched above you. You try to move, but your body does not follow. Unable to scream, you lie in bed paralyzed and terrified.

Maybe you have experienced sleep paralysis, but do you know what is really going on during an episode? Sleep can be categorized into two types: non-rapid eye movement (NREM) and rapid eye movement (REM). NREM sleep consists of stage 1, stage 2, stage 3, and stage 4; your body falls deeper into sleep during each stage. REM sleep is stage 5 of the sleep cycle and is characterized by vivid dreams and postural atonia. Postural atonia is the temporary paralysis of your voluntary muscles, such as your legs or your arms. This is necessary so that you do not hurt yourself by acting out your dreams. You can imagine how problematic it would be to act out a dream flying over the city when in reality you are jumping off your bed and belly-flopping onto the floor. Postural atonia prevents this danger through two parts of the brainstem, the pons and ventromedial medulla, which send inhibitory neurotransmitters down the spinal cord in order to suppress motor neurons, rendering us motionless.

Sleep paralysis occurs when you are perceptually alert, but still in a state of postural atonia from REM sleep. This means you are aware and able to use your five senses, but you are unable to move. Hallucinations, difficulty breathing, and fear are hallmarks of this mixed state of consciousness. Sleep paralysis hallucinations fall into three categories: intruder hallucinations, incubus hallucinations, and vestibular-motor hallucinations. Intruder hallucinations can range from the perception of a close friend to an evil presence entering the space where you sleep. Sometimes you can hear this friend or evil presence calling your name or talking to you and you are unable to respond, which can be frustrating. Incubus hallucinations involve an illusion of suffocation. These can often manifest themselves in the form of the evil presence sitting on your chest. You lie in bed looking at a demon-like presence that is crushing your body, causing you to feel like you cannot breathe, and sending you into a panic. Vestibular-motor hallucinations include out-of-body experiences (OBEs) and movement hallucinations. OBEs can include hovering above your bed while looking down at your sleeping body and the intruder. Movement hallucinations can include being dragged by the evil presence or falling, which is a common movement hallucination outside of sleep paralysis as well. But what is actually happening in the brain?

Let us zoom in to a region of the brain called the hypothalamus. The hypothalamus communicates with several parts of the brain. Some of these parts include a component of the brainstem called dorsal raphé nucleus (DRN), the amygdala, or the fear station of the brain, and the default mode network (DMN) which plays a role in creating self-identity. These three brain regions are hotspots for serotonergic neurons. Serotonin is a neurotransmitter involved in preventing REM sleep. Orexin neurons in the hypothalamus release a hormone called orexin to keep us awake during the day. Typically, when waking from sleep, those orexin neurons send a signal to the DRN. This signal then excites serotonin neurons to inhibit REM sleep and the associated postural atonia. However, during a sleep paralysis episode, the serotonergic neurons are stimulated too much. An overload of serotonin causes altered activity in the DRN, amygdala, and DMN. The DRN does not inhibit postural atonia, leaving your voluntary muscles paralyzed. Panic ensues due to increased activation of the amygdala. Serotonin rushes into the DMN and alters your perception of your self-identity, promoting OBEs and hallucinations of human-like figures. Together, a network is formed that results in your sleep paralysis dream.

So, what is the best way to deal with sleep paralysis? There are numerous factors that can bring on sleep paralysis episodes. Substance use, an inconsistent sleep schedule, stress, trauma, and genetic influences can all play a role. More research is needed to determine the causal mechanisms of these factors. However, there are several techniques individuals can use to lessen the panic response induced by sleep paralysis episodes.

One method to lessen the anxiety of sleep paralysis is to understand that the hallucinations are not real. Fortunately, your brain is more capable of realizing this in serotonergic hallucinations because they tend to be more “dream-like” than hallucinations brought on by other neurotransmitters. Slowing down and trying to take deep breaths can help the incubus hallucinations pass. Understanding the science behind what is occurring in your brain and body can help individuals understand that the intruder hallucinations and vestibular-motor hallucinations are merely a product of an irregular event in the brain and not a dangerous, threatening reality.

Next time you jolt awake to a demon-like presence sitting on your chest causing you to feel paralyzed, suffocated, and panicked I hope you can remember what is occurring in your brain. Your horrifying perception is simply a rush of serotonin that is overstimulating the DRN, amygdala, and DMN. Just remember: remain calm and it will pass.