Shadow people are a very common visual hallucination for humans to have. They usually appear as a result of sleep deprivation, psychosis (especially stimulant psychosis), delirium, psychoactive substances, or sleep paralysis. During this experience, the subject perceives a patch of shadow in their peripheral vision or focused visual field to be a living, autonomous figure. This figure can be either humanoid or animal-like in appearance and can be considered as a sub-type of autonomous entities.
The visual external hallucinations usually, but not always, begin to appear as initial fleeting images out of the corner of the eyes in the peripheral vision. As the duration of the experience (sleep deprivation, stimulant psychosis, diphenhydramine, etc.) progresses. However, shadow people may begin to appear in full view and one will be able to look directly at them. At advanced mental states, one is even able to look away from the entity and look back at the entity without a change in the hallucination. This progression is typically the same whether one is experiencing shadow people from sleep deprivation or from stimulant psychosis.
The bodies of the shadow people are usually perceived as a type of blackness that has a sense of depth with few facial or bodily features. The blackness of the body often seems almost opaque as if one is looking into a "black hole" in anthropomorphic form. They also may appear as animal forms, uniform blobs, disembodied body parts, or a myriad of indescribable shapes. They sometimes appear to have faces, eyes, or mouths and are able to move or change shape. The movement exhibited can be normal human movement or it can be faster, slower, or more choppy than a normal person's gait. It is also possible for multiple shadow people to occupy one's field of vision simultaneously while acting autonomously from one another and even interacting with one another.
This hallucinatory state is often accompanied by a feeling of intense paranoia and anxiety due to the fact that shadow people are subjectively sinister in appearance and usually a result of negative states such as stimulant psychosis and sleep paralysis. Shadow people appear often in sleep paralysis, often carrying with them a sense of impending doom during the experience
Although it is not an intrinsic part of this hallucinatory effect, shadow people can potentially be accompanied by other sensory components aside from one's visual perception of them. This is typically infrequent and usually only occurs during very intense states of sleep deprivation, delirium or psychosis. For example, shadow people can potentially have an accompanying "voice", despite the lack of a visible mouth structure. This auditory communication follows an identical leveling system of progressively more detailed and coherent spoken word in the same manner as a generic autonomous entity. Shadow people may converse with the person experiencing them or they may converse amongst each other - sometimes talking about the person going through the experience.
Alongside of accompanying auditory hallucinations, shadow people may also present tactile and gustatory hallucinations. This is even rarer than their potential auditory effects and typically only occurs in particularly intense and advanced hallucinatory states. Their tactile effects can be indistinguishable from a real human touch and generally varied in temperature.They can also even include physical actions such as pulling of clothing, hair, or the skin.
Shadow people have been referenced throughout popular culture and time as 'demons' or 'omens', 'ghosts', or even 'inter-dimensional time travellers". This wide recognition of shadow people, combined with their representation in common culture and horror films may contribute to the prevalence of these external hallucinations. It is worth noting that many people within the paranormal community genuinely believe that shadow people are actual ghosts or spirits rather than simple hallucinations.
The shadow person as an image was portrayed in the 20th-century show "The Twilight Zone", in the appropriately titled episode "The Shadow Man" where a shadow person lives under the main characters' bed. This episode was broadcast nationwide and still remains available, furthering people to exposure of shadow people through second-hand experiences and Hollywood-style manufactured images.
It seems the more an image is spread throughout a culture, the more likely it is that a person will manifest that image in a state such as sleep deprivation, delirium, and stimulant psychosis. The fear instilled by society through the culturally negative connotation associated with shadow people may influence the feelings anxiety and distress when seeing these autonomous entities. This has been investigated in relation to the common appearance of shadow people in sleep deprivation experiences.
Due to the cultural influence and the perception that shadow people may in fact be "spooky ghosts", many people who experience this external hallucination may attribute it to the paranormal or other irrational causes rather than accepting that it is a natural effect of abnormal brain chemistry that may stem from a wide variety of mental states. The de-stigmatising of the shadow person experience and rational discussion of the true origin of these autonomous entities could grant many sufferers relief from paranoia and mental illness stigma.
Compounds which may cause this effect commonly include:
Benzydamine, Datura, Diphenhydramine, Harmala alkaloid, Psilocin, Psilocybin mushrooms, Zolpidem