Myths of the Mahr

Here I am lying down to sleep;
No night mahr shall plague me
Until they have swum through all the waters
That flow upon the earth,
And count all the stars
That appear in the firmament.

— Westphalian prayer to ward off mahrs

For those who die in there sleep, the mahr are often the first to blame. Myths of the mahr hide in the dark bedtime tales that haunt children and adults alike. These myths are often believed to be true, making them even more terrifying.
It is not only people who are victims of the mahr. Horses have been known to be sleep-ridden by mahr. In the mornings these poor horses are covered in sweat, exhausted and their manes twisted in tangles. These tangles are also seem on people who are believed to have been tormented by a mahr, even if they do not remember it.
Trees are also beleved to have been tormented by mahrs, resulting in their branches being twisted and tangled. A certain type of pins that grows on coastal rocks and wet grounds as so often bothered by mahrs they are undersized and twisted. These poor trees are often called nightmare pines.

King Vanlandi

King Valandi had promised his wife Drifa that he would return within three years. After ten long years, Drifa went to the sorceress Hulda to lure King Valandi back to her or to kill him if that failed.
Alas for Vanlandi, the lure failed so Hulda summoned a mahr to assassinate him. The King had barely gone to sleep when he abruply complained aloud tha a mahr rode upon his chest. His men hurried to him but all they tried failed and Vanlandi died.

Mahr are thought to be heavy little creatures that sit on the chest of a sleeper and can only be seen in the sleeper's dreams.
It cannot be touched or moved as it haunted the sleeper with nightmares and, sometimes, death in their sleep.