Mora or Zmora in Slavic countries
according to wiki
In Polish folklore, mora are the souls of living people that leave the body during the night, and are seen as wisps of straw or hair or as moths. In certain Slavic languages, variations of the word mora actually mean moth (such as in Slovak language mora or another example is Czech word můra).
In Serbia, mare is called mora, or noćnik/noćnica ("night creature", masculine and feminine respectively). It is a common belief that mora enters the room through the keyhole, sits on the chest of the sleepers and tries to strangle them (hence moriti, "to torture", "to bother", "to strangle"). To repel moras, children are advised to look at the window or to turn the pillow and make a sign of cross on it (prekrstiti jastuk); in the early 19th century, Vuk Karadžić mentions that people would repel moras by leaving a broom upside down behind the door, or putting their belt on top of their sheets, or saying an elaborate prayer poem before they go to sleep.
In Croatian, "mora" refers to a "nightmare". Mora or Mara is one of the spirits from ancient Slav mythology. Mara was a dark spirit that takes a form of a beautiful woman and then visits men in their dreams, torturing them with desire, and dragging life out of them. Other names were nocnica, "night woman" in Polish, or éjjeljáró, "nightwalker" in Hungarian
from my family tales and personal experiences
it's lovely lady who sat on your chest in night and weep or chocke you she is really really upset and cold in touch she is or white or black more often called Zmora than Mora. She is undead unpeaceful soul who cries a lot