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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 and shadow people hauntings.

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Hypnagogia (also spelled hypnogogia) are the experiences a person can go through in the hypnagogic (or hypnogogic) state, the period of falling asleep. Hypnopompia are the experiences a person can go through in the hypnopompic state, the period of waking up. The term hypnagogia often encompasses hypnopompia as well. Hypnagogic sensations collectively describe the vivid dream-like auditory, visual, or tactile sensations that can be experienced in a hypnagogic or hypnopompic state. These sensations can be accompanied by sleep paralysis, the sensation that the body is temporarily paralyzed after waking or before falling asleep.

Hypnagogic sensations are vivid dream-like experiences that occur as one is falling asleep or waking up. Accompanying sleep paralysis can cause the sensations to be more frightening. The features of these sensations generally vary by individual, but some are more common to the experience than others:

Most common
Vividness
Fear
Falling sensation

Common
Sensing a "presence" (often malevolent)
Pressure/weight on body (especially the chest or back).
A sensation of not being able to breathe
Impending sense of doom/death

Fairly common
Auditory sensations (often footsteps or indistinct voices, or pulsing noises). Auditory sensations which are described as noise instead of sensations of legible sounds, are often described to be similar to auditory sensations caused by Nitrous Oxide by persons who have experienced both.
Visual sensations such as lights, people or shadows walking around the room

Less common
Floating sensations (sometimes associated with out-of-body experiences)
Seamless transition into fully immersive lucid dreaming, also associated with out-of-body experiences
Tactile sensations (such as a hand touching or grabbing)

Rare
Vibration
Involuntary movements (sometimes the feeling of sliding off of the bed or even up walls).
The feeling of being pulled in different directions

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