Hypnagogia

hypnagogichypnagogic hallucinationhypnagogic hallucinationshypnagogic statehypnogogicwaking dreamhypnagogic imageryhypnagogic statesearly stages of sleepfalling asleep
Hypnagogia, also referred to as "hypnagogic hallucinations", is the experience of the transitional state from wakefulness to sleep: the hypnagogic state of consciousness, during the onset of sleep (for the transitional state from sleep to wakefulness see hypnopompic).wikipedia
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Sleep paralysis

Phi Amold haghag ridden
Mental phenomena that may occur during this "threshold consciousness" phase include hallucinations, lucid thought, lucid dreaming, and sleep paralysis.
Sleep paralysis is when, during waking up or falling asleep, a person is aware but unable to move or speak.

Hallucination

hallucinationshallucinatehallucinating
Mental phenomena that may occur during this "threshold consciousness" phase include hallucinations, lucid thought, lucid dreaming, and sleep paralysis.
Hypnagogic hallucinations and hypnopompic hallucinations are considered normal phenomena.

Mental image

mind's eyevisualizationmental imagery
Among the more commonly reported, and more thoroughly researched, sensory features of hypnagogia are phosphenes which can manifest as seemingly random speckles, lines or geometrical patterns, including form constants, or as figurative (representational) images. Herbert Silberer described a process he called autosymbolism, whereby hypnagogic hallucinations seem to represent, without repression or censorship, whatever one is thinking at the time, turning abstract ideas into a concrete image, which may be perceived as an apt and succinct representation thereof.
There are sometimes episodes, particularly on falling asleep (hypnagogic imagery) and waking up (hypnopompic), when the mental imagery, being of a rapid, phantasmagoric and involuntary character, defies perception, presenting a kaleidoscopic field, in which no distinct object can be discerned.

Hypnopompic

hypnopompiahypnopompic hallucinationsduring waking up
Hypnagogia, also referred to as "hypnagogic hallucinations", is the experience of the transitional state from wakefulness to sleep: the hypnagogic state of consciousness, during the onset of sleep (for the transitional state from sleep to wakefulness see hypnopompic). The word hypnagogia is sometimes used in a restricted sense to refer to the onset of sleep, and contrasted with hypnopompia, Frederic Myers's term for waking up.
Its mirror is the hypnagogic state at sleep onset; though often conflated, the two states are not identical.

Tetris effect

Tetris'' effectGame Transfer Phenomenaphenomenon of the same name
People who have spent a long time at some repetitive activity before sleep, in particular one that is new to them, may find that it dominates their imagery as they grow drowsy, a tendency dubbed the Tetris effect.
In this sense, the Tetris effect is a form of hypnagogic imagery.

Form constant

form constants
Among the more commonly reported, and more thoroughly researched, sensory features of hypnagogia are phosphenes which can manifest as seemingly random speckles, lines or geometrical patterns, including form constants, or as figurative (representational) images.
Other triggers include psychological stress, threshold consciousness (hypnagogia), insulin hypoglycemia, the delirium of fever, epilepsy, psychotic episodes, advanced syphilis, sensory deprivation, photostimulation, electrical stimulation, crystal gazing, migraine headaches, dizziness and a variety of drug-induced intoxications.

Proprioception

proprioceptivekinestheticproprioceptors
Proprioceptive effects may be noticed, with numbness and changes in perceived body size and proportions, feelings of floating or bobbing as if their bed were a boat, and out-of-body experiences.
Similar effects can be felt during the hypnagogic state of consciousness, during the onset of sleep.

Herbert Silberer

SilbererSilberer, Herbert
Herbert Silberer described a process he called autosymbolism, whereby hypnagogic hallucinations seem to represent, without repression or censorship, whatever one is thinking at the time, turning abstract ideas into a concrete image, which may be perceived as an apt and succinct representation thereof.
He was very interested in dreams, and in 1909 published a paper detailing his research into the hypnagogic state (the mental state in which the individual is between waking and sleeping).

Sleep onset

falling asleeponset of sleepsleep onset REM periods
Hypnagogia, also referred to as "hypnagogic hallucinations", is the experience of the transitional state from wakefulness to sleep: the hypnagogic state of consciousness, during the onset of sleep (for the transitional state from sleep to wakefulness see hypnopompic).

Out-of-body experience

out-of-body experiencesout of bodyOut of Body Experience
Proprioceptive effects may be noticed, with numbness and changes in perceived body size and proportions, feelings of floating or bobbing as if their bed were a boat, and out-of-body experiences.
Other scientists have also linked OBEs to cases of hypnagogia and sleep paralysis (cataplexy).

Somnolence

drowsinesssleepinessDrowsy
People who have spent a long time at some repetitive activity before sleep, in particular one that is new to them, may find that it dominates their imagery as they grow drowsy, a tendency dubbed the Tetris effect.

Eigengrau

EigenlichtDark light (vision)visual noise
They are said to differ from dreams proper in that hypnagogic imagery is usually static and lacking in narrative content, although others understand the state rather as a gradual transition from hypnagogia to fragmentary dreams, i.e., from simple Eigenlicht to whole imagined scenes.

Sleep deprivation

deprived of sleepsleep deprivedlack of sleep
Microsleep (short episodes of immediate sleep onset) may intrude into wakefulness at any time in the wakefulness-sleep cycle, due to sleep deprivation and other conditions, resulting in impaired cognition and even amnesia.

Hypnic jerk

kickyou get that falling sensation
Perhaps the most common experience of this kind is the falling sensation, and associated hypnic jerk, encountered by many people, at least occasionally, while drifting off to sleep.

Rapid eye movement sleep

REM sleepREMrapid eye movement
It has been suggested that hypnagogia and REM sleep help in the consolidation of semantic memory, but the evidence for this has been disputed.
Narcolepsy by contrast seems to involve excessive and unwanted REM atonia—i.e., cataplexy and excessive daytime sleepiness while awake, hypnagogic hallucinations before entering slow-wave sleep, or sleep paralysis while waking.

Louis Ferdinand Alfred Maury

Alfred Maury
Serious scientific inquiry began in the 19th century with Johannes Peter Müller, Jules Baillarger, and Alfred Maury, and continued into the 20th century with Leroy.
He coined the term hypnagogic hallucination and reported a dream that famously inspired Salvador Dalí's painting [[Dream Caused by the Flight of a Bee Around a Pomegranate a Second Before Awakening]].

Jules Baillarger

BaillargerJules-Gabriel-François Baillarger
Serious scientific inquiry began in the 19th century with Johannes Peter Müller, Jules Baillarger, and Alfred Maury, and continued into the 20th century with Leroy.
In the field of psychiatry, Baillarger did research on the involuntary nature of hallucinations and the dynamics of the hypnagogic state (the intermediary stage between sleep and wakefulness).

Wakefulness

awakeawakeningwaking
Hypnagogia, also referred to as "hypnagogic hallucinations", is the experience of the transitional state from wakefulness to sleep: the hypnagogic state of consciousness, during the onset of sleep (for the transitional state from sleep to wakefulness see hypnopompic).

Sleep

sleepingsleep architectureasleep
Hypnagogia, also referred to as "hypnagogic hallucinations", is the experience of the transitional state from wakefulness to sleep: the hypnagogic state of consciousness, during the onset of sleep (for the transitional state from sleep to wakefulness see hypnopompic).

Consciousness

consciousconsciouslyhuman consciousness
Hypnagogia, also referred to as "hypnagogic hallucinations", is the experience of the transitional state from wakefulness to sleep: the hypnagogic state of consciousness, during the onset of sleep (for the transitional state from sleep to wakefulness see hypnopompic).

Lucid dream

lucid dreaminglucid dreamslucid
Mental phenomena that may occur during this "threshold consciousness" phase include hallucinations, lucid thought, lucid dreaming, and sleep paralysis.

Word sense

sensesensesbroader sense
The word hypnagogia is sometimes used in a restricted sense to refer to the onset of sleep, and contrasted with hypnopompia, Frederic Myers's term for waking up.

Frederic W. H. Myers

Frederic William Henry MyersF. W. H. MyersFrederic Myers
The word hypnagogia is sometimes used in a restricted sense to refer to the onset of sleep, and contrasted with hypnopompia, Frederic Myers's term for waking up.

Havelock Ellis

Henry Havelock EllisEllis, Havelockeonism
However, hypnagogia is also regularly employed in a more general sense that covers both falling asleep and waking up, and Havelock Ellis has questioned the need for separate terms.

Phenomenon

phenomenaphenomenalphysical phenomena
Indeed, it is not always possible in practice to assign a particular episode of any given phenomenon to one or the other, given that the same kinds of experience occur in both, and that people may drift in and out of sleep.