a grey bird flew past the window

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), 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. The hypnagogic state is sometimes proposed as an explanation for experiences such as alien abduction, apparitions, or visions. Formed in 2007.