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

The painting, based on a painting by Giulio Romano, shows a sleeping woman who has a demon sitting on her belly while a horse’s head pokes out of the canvas in the background of the scene. She was staging a fairly common sleep disorder: sleep paralysis .

What is sleep paralysis?

The dreamlike and dark setting of this work called The Nightmare makes the painting a perfect illustration of what could be one of the beasts of medieval European mythology: the incubus , a demon that is associated with the world of nightmares and that supposedly has sexual relations with women who, finding themselves between sleep and wakefulness, lie motionless without being able to do anything.

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

This disorder is called sleep paralysis , and Füssli’s picture expresses very well the sensations experienced while this curious phenomenon occurs.

What’s going on? 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 short 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 happening around them, with virtually no physical action. He will be able to perceive what is happening around him in the place where he has been put to rest, but he will not be able to move or ask for help.

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

Thus, it is common to have the feeling of suffocation or having 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 feeling 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 we know and which belong at least partially to the real world we have been in 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 world, the 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 responsible for sending commands to the muscles that can be controlled voluntarily. This means that, even if the person has regained consciousness and woken up, his or her muscles are still not “connected” to the brain, because they remain in the inert state that occurs during the REM phase of sleep, while we are dreaming.

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

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

Luckily, this is solved in a short time, usually within a few seconds. However, when 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 various studies on the prevalence of sleep paralysis indicate that these are rare cases considering the number of times a person goes to sleep in his or her lifetime, but the number of people who will experience this parasomnia at some point in their lives may be greater. Specifically, approximately 60% of the population may experience sleep paralysis .

However, the negative effects of sleep paralysis are found in the subjectivity and feelings experienced by the person experiencing it, so having read about this disorder may make the situation more bearable.

In any case, the fundamental thing 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 asphyxiation despite the fact that sometimes the lack of control over one’s movements generates this fear of stopping breathing (a process that is automated by the nervous system itself and does not depend on voluntary acts).

Bibliographic 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.