Hypnagogic

Hypnagogia is the experience of the transitional state from wakefulness to sleep: the ''hypnagogic'' state of consciousness, during the onset of sleep. Its opposite state is described as the transitional state from sleep into wakefulness. Mental phenomena that may occur during this "threshold consciousness" phase include hypnagogic hallucinations, lucid thought, exploding head syndrome, lucid dreaming, and sleep paralysis. The latter two phenomena are themselves separate sleep conditions that are sometimes experienced during the hypnagogic state.

Definitions

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. However, ''hypnagogia'' is also regularly employed in a more general sense that covers both falling asleep and waking up. 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. In this article ''hypnagogia'' will be used in the broader sense, unless otherwise stated or implied.

Other terms for hypnagogia, in one or both senses, that have been proposed include "presomnal" or "anthypnic sensations", "visions of half-sleep", "oneirogogic images" and "phantasmata", "the borderland of sleep", "praedormitium", "borderland state", "half-dream state", "pre-dream condition", "sleep onset dreams",Stickgold, R., interviewed 30 October 2000 by Norman Swan for '' The Health Report'' on Australia's Radio National
transcript
. Retrieved 3 July 2008. "dreamlets", and "wakefulness-sleep transition" (WST).

Threshold consciousness (commonly called "half-asleep" or "half-awake", or "mind awake body asleep") describes the same mental state of someone who is moving towards sleep or wakefulness but has not yet completed the transition. Such transitions are usually brief but can be extended by sleep disturbance or deliberate induction, for example during meditation.

Signs and symptoms

Transition to and from sleep may be attended by a wide variety of sensory experiences. These can occur in any modality, individually or combined, and range from the vague and barely perceptible to vivid hallucinations.

Sights

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. They may be monochromatic or richly coloured, still or moving, flat or three-dimensional (offering an impression of perspective). Imagery representing movement through tunnels of light is also reported. Individual images are typically fleeting and given to very rapid changes. 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. Descriptions of exceptionally vivid and elaborate hypnagogic visuals can be found in the work of Marie-Jean-Léon, Marquis d'Hervey de Saint Denys.

''Tetris'' effect

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. This effect has even been observed in amnesiacs who otherwise have no memory of the original activity. When the activity involves moving objects, as in the video game ''Tetris'', the corresponding hypnagogic images tend to be perceived as moving. The ''Tetris'' effect is not confined to visual imagery but can manifest in other modalities. For example, Robert Stickgold recounts having experienced the touch of rocks while falling asleep after mountain climbing. This can also occur to people who have travelled on a small boat in rough seas or have been swimming through waves, shortly before going to bed, and they feel the waves as they drift to sleep, or people who have spent the day skiing who continue to "feel snow" under their feet. People who have spent considerable time jumping on a trampoline will find that they can feel the up-and-down motion before they go to sleep. Many chess players report the phenomenon of seeing the chessboard and pieces during this state. New employees working stressful and demanding jobs often report feeling the experience of performing work-related tasks in this period before sleep.

Sounds

Hypnagogic hallucinations are often auditory or have an auditory component. Like the visuals, hypnagogic sounds vary in intensity from faint impressions to loud noises, like knocking and crashes and bangs ( exploding head syndrome). People may imagine their own name called, crumpling bags, white noise, or a doorbell ringing. Snatches of imagined speech are common. While typically nonsensical and fragmented, these speech events can occasionally strike the individual as apt comments on—or summations of—their thoughts at the time. They often contain word play, neologisms and made-up names. Hypnagogic speech may manifest as the subject's own " internal monologue, inner voice", or as the voices of others: familiar people or strangers. More rarely, poetry or music is heard.

Other sensations

Gustatory, olfactory and thermal sensations in hypnagogia have all been reported, as well as tactile sensations (including those kinds classed as paresthesia or formication). Sometimes there is synesthesia; many people report seeing a flash of light or some other visual image in response to a real sound. 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. 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.

Cognitive and affective phenomena

Thought processes on the edge of sleep tend to differ radically from those of ordinary wakefulness. For example, something that you agreed with within a state of hypnagogia may seem completely ridiculous to you in an awake state. Hypnagogia may involve a "loosening of ego boundaries ... openness, sensitivity, internalization-subjectification of the physical and mental environment (empathy) and diffuse-absorbed attention." Hypnagogic cognition, in comparison with that of normal, alert wakefulness, is characterized by heightened suggestibility, illogic and a fluid association of ideas. Subjects are more receptive in the hypnagogic state to suggestion from an experimenter than at other times, and readily incorporate external stimuli into hypnagogic trains of thought and subsequent dreams. This receptivity has a physiological parallel; EEG readings show elevated responsiveness to sound around the onset of sleep.

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.

The hypnagogic state can provide insight into a problem, the best-known example being August Kekulé’s realization that the structure of benzene was a closed ring while half-asleep in front of a fire and seeing molecules forming into snakes, one of which grabbed its tail in its mouth. Many other artists, writers, scientists and inventors – including Beethoven, Richard Wagner, Walter Scott, Salvador Dalí, Thomas Edison, Nikola Tesla

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