Rokurokubi

A creature from Japanese mythology. During the day it looks like an ordinary woman, but at night it turns into a vampire. The creature's head is capable of flying on a neck that stretches to an incredible length.

This head flies and drinks the blood of sleeping people, and sometimes it eats them completely. If the head of a creature is able to move separately from the body, without articulation with the neck, then such a spirit is called a Nukekubi.