She rides your chest as you sleep, darkening your dreams.
The mara are wraiths who brought terrible dreams across the Scandinavian and Germanic lands. They came into bedrooms through keyholes and the cracks under doors to sit upon the chest of a sleeper. If you end up with one of these spirit-ladies on your chest, your dreams will be haunted by their twisted darkness. Sleep on your side if you can – you don’t want a mara finding your chest tonight.
Image – The Nightmare by John Henry Fuseli on Wikimedia Commons