In Slavic mythology, notsnitsa (Belarusian: начніца, romanized: načnica, Polish: nocnica, płaczka, Bulgarian: горска майка, ношно, romanized: gorska majka, nošno, Serbian: шумска маjка, бабице, ноћнице, romanized: šumska majka, babice, noćnice, Croatian: mrake, vidine, Slovene: nočnine, mračnine, Ukrainian: нічниця, romanized: nichnytsia, Russian: ночница, romanized: nochnitsa), often referred in plural, is a nightmare spirit or demon that torments people and especially children at night. Other names for notsnitsa in East Slavic languages include kriksy, plaksy, plachky, plaksivicy, kriksy-varaksy, kriksy-plaksy, night hag, night maiden.

In Russian and Slovak folklore, notsnitsa are known to torment children at night, and a stone with a hole in the center is said to be a protection from nocnitsa. Mothers in some regions will place a knife in their children's cradles or draw a circle around the cradles with a knife for protection. This is possibly based on the belief that supernatural beings cannot touch iron.

Nocnitsa is known to sit on one's chest, drawing "life energy". Because of this, many refer to nocnitsa as a type of vampire. Nocnitsa will often continue visiting. According to some folklore, night hags visit when one sleeps on one's back, with the hands on the chest (a position allegedly called "sleeping with the dead"). According to some folklore, night hags are made of shadow. She might also have a horrible screeching voice.^{[citation needed]} She might allegedly also smell of the moss and dirt from her forest of origin.^{[citation needed]}

Nocnitsa is linked to the common apparition seen during the hypnagogic state of sleep.^{[citation needed]}