In Japanese folklore, a nukekubi is a severed head that flies through the night.
Nukekubi stories describe a person whose head separates from the body while sleeping and travels independently. The flying head may attack or frighten people before returning to the body before dawn. The name literally refers to a detached or severed neck.
Nukekubi is closely related to the rokurokubi, another Japanese supernatural figure whose head or neck separates or stretches. English-language summaries sometimes merge the two, but the traditions are commonly distinguished by the degree and manner of separation.
These stories belong to the wider yōkai tradition recorded and reshaped in literature, illustrated collections, and later popular culture. They are folklore motifs rather than descriptions of a medically documented condition.