A beginner's guide to Hypnogogia

Hypnogogia is used to refer to the onset of sleep, and contrasted with hypnopompia, which is the term for waking up. 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.

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.

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). 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.

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 computer game Tetris, the corresponding hypnagogic images too tend to be perceived as moving. The Tetris effect is not confined to visual imagery, but can manifest in other modalities also. For example, people who have travelled on a small boat in rough seas, or swam in 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.

Hypnagogic imagery is often auditory or has an auditory component. Like the visuals, hypnagogic sounds vary in intensity from faint impressions to loud noises, such as crashes and bangs. People may imagine their own name called 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 wordplay, neologisms and made-up names. Hypnagogic speech may manifest as the subject’s own ‘inner voice’, or as the voices of others: familiar people or strangers. More rarely, poetry or music is heard.

Humming, roaring, hissing, rushing and buzzing noises are frequent in conjunction with sleep paralysis (SP). This happens when the REM atonia sets in sooner than usual, before the person is fully asleep, or persists longer than usual, after the person has (in other respects) fully awoken. SP is reportedly very frequent among narcoleptics. It occurs frequently in about 6% of the rest of the population, and occurs occasionally in 60%. In surveys, 20 to 60% of individuals reported having experienced SP at least once in their lifetime.The paralysis itself is frequently accompanied by additional phenomena. Typical examples include a feeling of being crushed or suffocated, electric ‘tingles’ or ‘vibrations’, imagined speech and other noises, the imagined presence of a visible or invisible entity, and sometimes intense emotion: fear or euphoria and even orgasmic feelings. SP has been proposed as an explanation for at least some alien abduction experiences and shadow people hauntings.

Gustatory (taste), olfactory (smell) and thermal sensations in hypnagogia have all been reported, as well as tactile sensations (including those kinds classed as paraesthesia). Sometimes there is synaesthesia (sensation in one part of the body brought about by stimulus to another); 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, 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.

Hypnagogic phenomena may be interpreted as visions, prophesies, premonitions, apparitions and inspiration (artistic or divine), depending on the experiencer’s beliefs and those of their culture.

Thought processes on the edge of sleep tend to differ radically from those of ordinary wakefulness. 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 characterised by heightened suggestibility, illogic and 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.

Sleep researchers have 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.

A feature that hypnagogia shares with other stages of sleep is amnesia. But this is a selective forgetfulness, affecting the hippocampal memory system, which is responsible for episodic or autobiographical memory, rather than the neocortical memory system, responsible for semantic memory. It has been suggested that hypnagogia and REM sleep help in the consolidation of semantic memory, but the evidence for this has been disputed. For example, suppression of REM sleep due to antidepressants and lesions to the brainstem has not been found to produce detrimental effects on cognition.

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, amnesia.

Daytime parahypnagogia (DPH), is the spontaneous intrusion of a flash image or dreamlike thought or insight into one’s waking consciousness. DPH is typically encountered when one is “tired, bored, suffering from attention fatigue, and/or engaged in a passive activity.” The exact nature of the episode may be forgotten even though the individual remembers having had such an experience. DPH can be defined as disassociative, trance-like, but, unlike a daydream, not self-directed” – however, daydreams and waking reveries are often characterised as “passive,” “effortless,”and “spontaneous,” while hypnagogia itself can sometimes be influenced by a form of autosuggestion, or “passive concentration,” so these sorts of episode may in fact constitute a continuum between directed fantasy and the more spontaneous varieties of hypnagogia. Others have emphasised the connections between fantasy, daydreaming, dreams and hypnosis.

Investigative methodology into hypnogogic states mainly involve self-observation (spontaneous or systematic) and this was the primary tool of the early researchers. In the late 20th and early 21st centuries, this has been joined by questionnaire surveys and experimental studies. All three methods have their disadvantages as well as points to recommend them.

Naturally, amnesia contributes to the difficulty of studying hypnagogia, as does the typically fleeting nature of hypnagogic experiences. These problems have been tackled by experimenters in a number of ways, including voluntary or induced interruptions, sleep manipulation, the use of techniques to “hover on the edge of sleep” thereby extending the duration of the hypnagogic state, and training in the art of introspection to heighten the subject’s powers of observation and attention.

Techniques for extending hypnagogia range from informal ones (e.g. the subject holds up one of their arms as they go to sleep, so as to be awakened when it falls), to the use of biofeedback devices to induce a ‘theta’ state, characterised by relaxation and theta EEG activity. The theta state is produced naturally the most when we are dreaming. It has also been linked to paranormal activities and is believed to trigger the release of DMT from the pineal gland, causing a dreaming state. Another method is to induce a state said to be subjectively similar to sleep onset in a Ganzfeld setting, a form of sensory deprivation. But the assumption of identity between the two states may be unfounded. The average EEG spectrum in Ganzfeld is more similar to that of the relaxed waking state than to that of sleep onset. Studies have concluded that “the Ganzfeld imagery, although subjectively very similar to that at sleep onset, should not be labeled as ‘hypnagogic’. Perhaps a broader category of ‘hypnagoid experience’ should be considered, covering true hypnagogic imagery as well as subjectively similar imagery produced in other states.”