Originally attributed to nightmares because of what they'd experienced, the deaths were not restricted to Cambodian refugees. Since that time, evidence has accumulated that sleep deaths resulted from a genetic heart condition called Brugada syndrome.
Rapid-eye movement, or REM, sleep occurs when people are in the deepest sleep, at the time when they dream.
"If people have cardiac disease, they would naturally be more at risk in REM sleep than even being awake," said Basner. "It's not the dream itself, it's the fact that they're in REM sleep."
During REM sleep, the heart rate is less stable than it would normally be, and so it can present a danger to a patient with heart trouble.
"If you have heart disease, REM sleep is a very challenging time," said Basner.
Shortly after the discovery of REM sleep in the 1950s, an episode of "The Twilight Zone," "Perchance to Dream," centered on a man who was afraid to sleep because of dreams of a woman who sought to kill him.
But Basner explained that the fate of the man in the episode (SPOILER ALERT), he suffered a heart attack in his sleep, revealed the futility of trying to avoid sleep to avoid the nightmares, since a sleep-deprived person is likely to rebound into REM sleep once getting to sleep.
"You can't cure that by trying to stay awake," he said, praising the accuracy of the episode.
Heart problems are not the only ones that can emerge when asleep
Avidan explained that some people have difficulty breathing in their sleep and may need pressure on their airways to prevent choking.
In the end, one of the biggest sleep myths may be that sleep is always a benign and restful state.