Sleep Paralysis | Common Sleep Paralysis | Hallucinatory sleep paralysis

Sleep Paralysis

Sleep Paralysis Overview

Sleep paralysis is a condition characterized by paralysis of the body shortly after waking up (known as hypnopompic paralysis) or, less often, shortly before falling asleep (known as hypnagogic paralysis).

Sleep paralysis may also be referred to as isolated sleep paralysis, familial sleep paralysis, hynogogic or hypnopompic paralysis, predormital or postorbital paralysis. Physiologically, it is closely related to the normal paralysis that occurs during REM sleep, also known as REM atones.

Normal sleep paralysis is thought to be due to mechanisms in the brain stem, particularly the vestibular, reticular, and oculomotor neurons, which prevent bodily movements, block sensory input and provide the forebrain with the internally generated activity that characterizes brain activity during REM sleep.

This is thought to be necessary to prevent the body from movements caused by dreams. Eyes however are not paralyzed by this system. Sleep paralysis is a frightening form of paralysis that occurs when a person suddenly finds himself or herself unable to move for a few minutes, most often upon falling asleep or waking up.

Sleep paralysis is due to an ill-timed disconnection between the brain and the body. Sleep paralysis occurs when the brain is awakened from a REM state into essentially a normal fully awake state, but with the bodily paralysis still occurring.

This causes the person to be fully aware, but unable to move. In addition, this state is usually accompanied by certain specific kinds of hallucinations. This state usually lasts no more than two minutes before a person is able to either return to full REM sleep or to become fully awake.

The features of these hallucinations generally vary by individual, but some are more common to the experience than others. There are two major types of sleep paralysis: common (typical) also known as CSP and hallucinatory (hypnagogic) sleep paralysis known as HSP.

What is exactly happening in the brain during sleep paralysis?

During sleep, we go through different stages of sleep. Rapid Eye Movement (REM) stage is the stage where dreaming occurs. In this stage, a mechanism is created that protects us from acting our dreams; this is called “muscular atonia”.

Muscular atonia basically means that all the muscles in our body will be suppressed during REM sleep (except the diaphragm and muscles of the eyes). This atonia comes to an end when we move to another stage of sleep or upon awakening.

But at times something goes wrong; the person wakes up during REM sleep and this protective mechanism “atonia” does not come to an end. This creates an incapability to move (paralysis), and as the brain was just dreaming, this may result in terrifying hallucinations.

Differences between Common Sleep Paralysis and Hallucinatory (hypnagogic) sleep paralysis.

  • Common Sleep Paralysis is only unnerving for the sleeper but Hallucinatory sleep paralysis is accompanied by a nightmare like hallucination.
  • Common Sleep Paralysis is of relatively short duration where Hallucinatory sleep paralysis can last as long as seven or eight minutes.
  • Common Sleep Paralysis is common and universal; Hallucinatory sleep paralysis is rare and seems to be geographically episodic.

One of the most important differences between Night Terrors and Common Sleep Paralysis is that Common Sleep Paralysis occurs in Stage one of sleep and Night Terrors occur in stage four.

Is Sleep Paralysis harmful?

Sleep paralysis is most often related with narcolepsy, a neurological condition in which the person has uncontrollable naps. Narcolepsy is a sleep disorder characterized by irresistible and uncontrollable attacks of sleepiness. However, there are many persons who experience sleep paralysis without having signs of narcolepsy.

Sometimes it runs in families. It is not harmful, although most people report feeling very terrified because they do not know what is happening, and within minutes they slowly or rapidly are able to move again; the event is often terminated by a sound or a touch on the body. All patients with sleep paralysis and narcolepsy need medical attention and treatment.

In some cases, when hypnogogic hallucinations are present, people feel that someone is in the room with them; some experience the feeling that someone or something is sitting on their chest and they feel imminent death and suffocation. That has been called the “Hag Phenomena” and has been occurring to people over the centuries. These things cause people much anxiety and fear, but there is no physical harm. Patients should know that this disorder is benign and does not put at risk their life at all.


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