Hypnagogia

Sleep paralysis, scientifically known as hypnagogia, is a lively illustrative experience that occurs at the beginning of the sleep cycle. In addition, hypnagogic hallucinations are truly lively dreams full of visual, tactile, and auditory phenomena. Hypnopumpic hallucinations, on the other hand, are similar experiences that occur when a person wakes up.

This term, created by Frederic WH Myers and consisting of the words Hypnos  (sleep) and pomp  (send), was first used in 1918 in connection with hypnopompous hallucinations. In addition to this, it was intended to describe a phenomenon that occurred during the transition period of sleeping and waking.

Hypnagogic hallucinations were first described by the French psychiatrist Baillarger in 1846. He also called them psychosensory hallucinations. Moreover, according to Alfred Maury, the terms Hypnos  (sleep) and  agogos (induced) mean hallucinations or delusions that reveal  sleep.

Thus, these hallucinations appear when a person believes they are awake. He can see, hear and feel, but not move. In addition, hypnagogic hallucinations are closely associated with sleep paralysis.

Incidence and history of hypnagogic hallucinations

The incidence of hypnagogic and hypnapompous hallucinations is 25–30% of those with narcolepsy (2). In 1957, researchers Yoss and Daly included these hallucinations in the diagnostic criteria for narcolepsy. These hallucinations are also characterized by excessive daytime sleep disorders. These were observed in patients who experienced sleep paralysis before falling asleep (3.4).

In addition, psychoactive substances such as khat (5) and hashish (6) cause both hypnogogic and hypnopumpic hallucinations.

Hypnagogic and hypnagogic hallucinations

Sleep paralysis consists of a general and transient inability to move or speak. Eventually, it occurs during the transition phase of sleep and awakening, when hypnagogic hallucinations occur.

Long ago, sleep paralysis and hypnagogic hallucinations were important features of nightmares. Popular culture embellished these symptoms with supernatural meanings. thus, some believed that hypnagogy and hallucinations were caused by demons.

In 1834, McNish first described nightmares as follows:

As you read this, and other similar stories, you may notice that the term “nightmare” has changed over the last 150 years. Today, it means a really lively, unpleasant sleep that causes fear and numerous awakenings.

Incubus: a nocturnal demon

In his book On the Nightmare, Ernest Jones explains that the word nightmare originally meant  “Incubus”  (a male demon). According to local folklore, such a nocturnal demon was responsible for horrific experiences in dreams.

Incubus is a demon who, according to a well-known European medieval methodology, climbed over sleeping women and attacked them. According to legend, the purpose of this demon was to rape them, sometimes with the intention of making women pregnant, as the Merlin legend states (8). The feminine opponent of Incubus that climbs on top of sleeping men is called Succubus. 

People believed that Incubus visited people at night and settled on their chests so they couldn’t move. Jones points out that this belief was almost universal. Thus, this would mean that hypnagogic hallucinations would be caused in some way by nocturnal demons.

Finally, these hallucinations are currently being studied as symptoms of narcolepsy. However, they also occur in healthy people. (9)