Back in the 1970s, several patients in an experimental sleep study reported seeing shadowy intruders. These patients, and hundreds of others, died in their sleep soon after. Doctors called the phenomenon ''Sudden Unexplained Nocturnal Death Syndrome''. They refused to discuss the shadows. Now, a struggling late night radio host and a skeptical CDC investigator have begun researching a disturbing new outbreak of shadowy sightings and sleep fatalities. Could this be a case of paranoid hallucination, or are these victims literally being scared to death by actual nightmare creatures?