The idea of dying in an alternate reality causing actual death is something out of an '80s horror movie and then again in a '90s sci-fi action thriller …
... or is it? In 2014, Wes Craven revealed that his inspiration for A Nightmare on Elm Street came in part from an L.A. Times article about a young man plagued by nightmares after escaping the Killing Fields in Laos. He eventually stopped sleeping, telling his family that "he was afraid that if he slept, the thing chasing him would get him." After he eventually succumbed, his family "heard screams in the middle of the night, [and] by the time they got to him, he was dead. He died in the middle of a nightmare."
Coincidence? Maybe. In fact, it's hard to find that particular story in the L.A. Times archive, so it's possible that Craven unknowingly invented these details over the decades, but the newspaper really did run a series of articles in the early '80s about an epidemic of healthy young Southeast Asian refugees who mysteriously died of sudden cardiac arrest after screaming in their sleep.
Several theories have been proposed over the years to explain the deaths in a non-spooky way, but none of them are quite satisfactory. The refugee community themselves believed it was probably a side effect of chemical warfare, but no sign of poisoning was evident in the victims, although symptoms of night terrors were. It's also a phenomenon that, while less prevalent, goes back to at least 1917. And it doesn't really explain the screaming.
In 1987, a Chicago medical examiner studying the case found that all the victims appeared to have enlarged hearts and other cardiac anomalies that probably contributed to their deaths. He theorized that "something" spontaneously "overloaded these defective hearts, causing the sudden deaths," which could be anything from "a random electronic discharge" to "yes, perhaps a nightmare." There does seem to be a genetic component to the phenomenon, which predominantly affects people from Southeast Asia, so you're probably safe unless you have some kind of heart defect that, again, can go entirely undetected until you die screaming. Sleep tight!
Top image: New Line Cinema