Actually there is actually a documented disease called SUNDS. Sudden Unexpected Nocturnal Death Syndrome. It affects people mostly documented in the Phillipines, but is genetic amongst the populations of other races, affecting 42 of 100,000 Philippine people each year, most of them young adult males. They go into a random cardiac arrest or irregular heart rhythyms and die in thier sleeps, sometimes described by survivors as demonic nightmares.
Makes you not wanna sleep alone anymore huh?