Sleep paralysis: definition, symptoms and causes

We explain what this unique sleep disorder consists of.

At the end of the 18th century, the painter Johan Heinrich Füssli Johan Heinrich Füssli completed one of his most emblematic works.

The painting, based on a painting by Giulio Romano, depicts a sleeping woman with a demon sitting on her belly while a horse's head peeks through the fabrics that form the backdrop for the scene. It staged a fairly common sleep disorder: sleep paralysis..

What is sleep paralysis?

The dreamlike and dark setting of this play called The Nightmare makes the painting a perfect illustration of what could be one of the beasts of the medieval European mythology: the incubusa demon who is associated with the world of nightmares and who supposedly has sexual relations with women who, when they find themselves between sleep and wakefulness, lie motionless and unable to do anything.

Today, some researchers believe that the mythology behind the figure of the incubus and his female alter ego, the succubus, is actually a supernatural interpretation of a perfectly scientifically documented sleep disorder.

This disorder is called sleep paralysisand Füssli's picture expresses very well the sensations experienced during this curious phenomenon.

What happens? Symptoms

The name sleep paralysis is quite descriptive: Is a sleep disorder in which the person is unable to perform any voluntary movement.. This means that, for a brief period of time, someone experiencing sleep paralysis will go through a state of consciousness between sleep and wakefulness and will only be able to see what is going on around them, with virtually no physical actions. He will be able to perceive what is going on around him in the place where he has come to rest, but he will not be able to move or call for help.

Of course, sleep paralysis does not affect vital functions such as breathing and heartbeat, since these movements are involuntary. However, this does not detract from the fact that it is a very unpleasant and anxiety-generating sensation, among other things because it usually goes hand in hand with the sensation of not being able to breathe well (not being able to control the vocal cords well, it seems that the air escapes from the lungs without being able to do anything to remedy it).

Thus, it is common to have the sensation of suffocation or difficulty breathing, but this is only a consequence of not being able to consciously control the muscles, and there is no real risk of drowning.

Sleep paralysis can occur with other factors of a subjective nature, such as hallucinations or the sensation of having strange or threatening presences nearby that haunt the paralyzed person.

This is mainly because it appears in a transitional phase between sleep and wakefulness, and makes these hallucinations seem more real, occurring in places that we know and that belong at least partially to the real world in which we have been lately. For example, at first we may realize that we are in the bed in which we went to bed last night and therefore in the real, waking world, but then strange elements appear that are not possible in real life, such as levitating sheets, monsters, etc.

Common causes

In general terms, sleep paralysis is due to a lack of coordination between some areas of the brain and the part of the nervous system in charge of sending orders to the muscles that can be controlled voluntarily. that can be controlled voluntarily. This means that, although the person has regained consciousness and has woken up, his or her muscles are still not "connected" to the brain, because they are still in the inert state that occurs during the REM sleep phase, while we dream.

During the REM phaseThe fact of having the muscles isolated from what happens in our consciousness is useful, because otherwise we would move our body according to everything that happens in our dreams.

However, this usefulness disappears in cases of sleep paralysis and the mechanism responsible for separating muscles and consciousness turns against us, since we experience what has to do with wakefulness and sleep: the hallucinations typical of dreams, and the immobility of the physical world in which we are actually sleeping.

Fortunately, this is resolved in a short time, usually after a few seconds. However, as this phenomenon appears in a state of transition between wakefulness and sleep, the perception of time may be somewhat altered.

In any case, the exact causes of this phenomenon are not entirely clear, and much research remains to be done to understand its mechanisms.

Who can this happen to?

The different studies on the prevalence of sleep paralysis indicate that they are rare cases considering the number of times a person goes to sleep during his or her lifetime, but the number of people who will experience this parasomnia at some point in their lives could be in the majority. Specifically, approximately 60% of the population may experience sleep paralysis at some point in their lives..

However, the negative effects of sleep paralysis lie in the subjectivity and sensations experienced by the person experiencing it, so having read something about this disorder could make this situation more bearable.

In any case, what is fundamental is that although sleep paralysis is usually experienced in an unpleasant way, in normal situations it does not constitute a source of danger, nor does it lead to asphyxia, although sometimes the lack of control over one's own movements generates this fear of stopping breathing (a process automated by the nervous system itself and which does not depend on voluntary acts).

Bibliographical references:

• American Sleep Disorders Association (1990). International Classification of Sleep Disorders: diagnostic and Coding Manual, In Press.
• Cheyne, J. (2003). "Sleep Paralysis and the Structure of Waking-Nightmare Hallucinations". Dreaming. 13 (3): 163–179.
• Jalal, B.; Simons-Rudolph, J.; Jalal, B.; Hinton, D. E. (2014). "Explanations of sleep paralysis among Egyptian college students and the general population in Egypt and Denmark". Transcultural Psychiatry. 51 (2): 158-175.
• Teculescu, D.B.; Mauffret-Stephan, E., Gaultier, C.: Familial predisposition to snoring. (Letter) Thorax, 1994.