Sleep paralysis is a common condition characterized by transient partial or total paralysis of skeletal muscles and areflexia that occurs upon awakening from sleep or less often while falling asleep. Stimuli such as touch or sound may terminate the episode, which usually has duration of seconds to minutes.
The incidence of isolated sleep paralysis was, as per previous reports, higher in African-Americans.
Paralysis: this occurs after waking up or shortly before falling asleep. The person cannot move any body part, cannot speak, and only has minimal control over blinking and breathing. This paralysis is the same paralysis that occurs when dreaming. The brain paralyzes the muscles to prevent possible injury during dreams, as some body parts may move during dreaming. If the person wakes up suddenly, the brain may still think that it is dreaming, and sustains the paralysis.
Images or speaking that appear during the paralysis. The person may think that someone is standing beside them or they may hear strange sounds. These may be dreamlike, possibly causing the person to think that they are still dreaming. Often it is reported as feeling a weight on one's chest, as if being underneath a person or heavy object.
Physiologically, it is closely related to the paralysis that occurs as a natural part of REM (rapid eye movement) sleep, which is known as REM atonia. Sleep paralysis occurs when the brain awakes from a REM state, but the bodily paralysis persists. This leaves the person fully conscious, but unable to move. In addition, the state may be accompanied by terrifying hallucinations (hypnopompic or hypnagogic) and an acute sense of danger.
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 from Canada, China, England, Japan and Nigeria, 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 orgasmic feelings. SP has been proposed as an explanation for at least some alien abduction experiences.
States of awareness may be distinguished from the dream experiences typically reported; these include dreamlike states experienced as a person falls asleep and as he awakens, respectively called hypnagogic and hypnopompic reveries. During sleep itself there are nightmares, observable signs of sexual activity, and sleepwalking. Even people who ostensibly are awake may show evidence of such...
hallucinations ( in hallucination: Hypnagogic hallucinations )
Common hypnagogic hallucinations may be visual (e.g., scenes from the previous few hours appear) or auditory (e.g., one seems to hear one’s name called). A frequently occurring hypnagogic hallucination is the sensation of loss of support or balance, perhaps accompanied by a fragmentary “dream” of falling, followed immediately by a jerking reflex recovery movement
Theosophical Society Relation to Sleep Paralysis as the "Dweller of the Threshold"
The Guardian of the Threshold is a menacing figure that is described by a number of leading esoteric teachers,    The term "Guardian of the Threshold", often called "dweller on the threshold" indicates a spectral image which is supposed to manifests itself as soon as "the student of the spirit ascends upon the path into the higher worlds of knowledge"
According to Max Heindel, the Dweller on the Threshold (also called Guardian of the Threshold), which every aspirant has to meet -usually at an early stage of his progress into the unseen worlds- is one of the causes of main causes of obsession of men interested in occultism.
"This Dweller of the Threshold meets us in many shapes. It is the Cerberus guarding the entrance to Hades; the Dragon which St. Michael (spiritual will-power) is going to kill; the Snake which tempted Eve, and whose head will be crushed by the heel of the woman; the Hobgoblin watching the place where the treasure is buried, etc. He is the king of evil, who will not permit that within his kingdom a child should grow up, which might surpass him in power; the Herod before whose wrath the divine child Christ has to flee into a foreign country, and is not permitted to return to his home (the soul) until the king (Ambition, Pride, Vanity, Self-righteousness, etc.) is dethroned or dead."
Ethiopian Culture Relation to Sleep Paralysis as "Dukak"
In Ethiopian culture the word Dukak is used. Dukak is believed to be some form of evil spirit that possesses people during their sleep. This experience is also believed to be related to use of Khat. Khat chimical make up includes Norepinephrine which is a precursor to Dopamine. Neropinehrin supports and prolongs REM sleep and supports similar results as acetylcholine precursors.
Egyptian Relation to Sleep Paralysis as "Apep"
On the occasions when Apep was said to have been killed, he was able to return each night.
Apep was not so much worshipped, as worshipped against. His defeat each night, in favour of Ra, was thought to be ensured by the prayers of the Egyptian priests and worshipers at temples. The Egyptians practiced a number of rituals and superstitions that were thought to ward off Apep, and aid Ra to continue his journey across the sky.
Scandinavian Folklore Relation to Sleep Paralysis as the "Mara"
Mare is a kind of malignant female wraith in Scandinavian folklore believed to cause nightmares
The mara was thought of as an immaterial being – capable of moving through a keyhole or the opening under a door – who seated herself at the chest of a sleeping person and "rode" him or her, thus causing nightmares. The word nightmare is a compositon of the word Mara and Night.
Brittish and Anglophone North American folklore Relation to Sleep Paralysis as the "Old Hag"
According to folklore, the Old Hag sat on a sleeper's chest and sent nightmares to him or her. When the subject awoke, he or she would be unable to breathe or even move for a short period of time.
Neurobiology Relation to Sleep Paralysis as the "Old Hag Syndrom"
The expression Old Hag Attack refers to a hypnagogic state in which paralysis is present and, quite often, it is accompanied by terrifying hallucinations. When excessively recurrent, some consider them to be a disorder; however many populations treat them as simply part of their culture and mythological world-view, rather than any form of disease or pathology.
Night terrors happen during deep non-REM sleep. Unlike nightmares (which occur during REM sleep), a night terror is not technically a dream, but more like a sudden reaction of fear that happens during the transition from one sleep phase to another.
Night terrors typically occur about 2 or 3 hours after a child falls asleep, when sleep transitions from the deepest stage of non-REM sleep to lighter REM sleep, a stage where dreams occur. Usually this transition is a smooth one. But rarely, a child becomes agitated and frightened — and that fear reaction is a night terror.
Conclusion of Sleep Paralysis:
As anyone can see there has been a long history of hallucinations and SP relations during sleep stages in human history. There is a strong correlation to religiouse belifes of demons or other type of spherical encounters that can be easily explained by the occurrences of non dream state type hallucinations. In the relation to sleep paralysis, it can be concluded from the historical evidence of SP that SP can contain both hallucinations with and without the paralysis.
Since SP is related to the hypnagogic state of mind, then the hallucinations most likely are caused by the hypnagogic states of mind rather than the SP itself. Since hypnagogic state of mind is present in non-REM status as well as moving from REM to other sleep stages, SP and hypnogogia type of hallucinations can be related to non-REM to REM transitions. Night Terrors are also experienced during this non-REM transition as well as deep sleep. With this relation, NT has a strong correlation as being the same hypnogogic hallucination as experienced during SP. Nightmares are also hypnogogic hallucinations since the word nightmare is composed from the Scandinavian Folklore word "Mara."
Wake Induced Lucid Dreaming (WILD) shows the same type of hallucinations during the conscious transition from waking states to dreaming.
**I need to research more about drugs and their relation to hypnogogic states of hallucinations.