<Tr> <Th_colspan="2"> Classification and external resources </Th> </Tr> <Tr> <Th> Specialty </Th> <Td> Sleep medicine </Td> </Tr> <Tr> <Td_colspan="2"> (edit on Wikidata) </Td> </Tr> <P> A hypnic jerk, hypnagogic jerk, sleep start, sleep twitch or night start is an involuntary twitch which occurs when a person is beginning to fall asleep, often causing them to awaken suddenly for a moment . Physically, hypnic jerks resemble the "jump" experienced by a person when startled, sometimes accompanied by a falling sensation . Hypnic jerks are associated with a rapid heartbeat, quickened breathing, sweat, and sometimes "a peculiar sensory feeling of' shock' or' falling into the void"'. A higher occurrence is reported in people with irregular sleep schedules . </P>

Why do we sometimes feel like we are falling in our sleep