Hypnagogia

Overview
Hypnagogia (also spelled hypnogogia) describes vivid dreamlike auditory, visual, or tactile sensations, which are often accompanied by sleep paralysis and experienced when falling asleep as opposed to the hypnopompic state leading to waking up.

Hypnagogic sensations
The hypnagogic experience occurs between being awake and asleep, while the hypnopompic experience occurs as one is waking up; both experiences occur within the time period between sleep and waking (or vice versa). Experienced qualities vary, and include fear, awareness of a "presence," chest or back pressure, an inability to breathe (hence the folkloric notion of mara-like creatures tormenting sleepers), and a falling sensation or a feeling of tripping (as hypnic jerks are interpreted by the brain). Exploding head syndrome may also be experienced, or just an overwhelmingly loud sound.

During the hypnagogic state, an individual may appear to be fully awake, but has brain waves indicating that the individual is technically sleeping. Also, the individual may be completely aware of their state, which enables lucid dreamers to enter the dream state consciously directly from the waking state (see wake-initiated lucid dream technique).

The hypnagogic state is sometimes proposed as an explanation of experiences such as alien abduction, apparitions, or visions.