It's the stuff of horror movies.
The sleeping hero sits bolt upright in bed, breathing hard and eyes wide open. Suddenly he explodes into a blood-curdling scream.
The official term for it is "night terror," and one of the more unusual things about this behavior is that the sleeper continues to snooze right through it.
According to the Mayo Clinic, night terrors occur most frequently in childhood. Causes may include stress, fatigue, fever, lights or noise. In adults, the causes may also include sleep apnea, migraines, head injuries, alcohol, illegal drugs or certain other medications.
There is another sleep oddity of which even more of us may be aware: sleepwalking.
Dr. Michael Coats, a board-certified neurologist specializing in sleep medicine at the Kootenai Clinic, said, "From a neurological point of view, we divide sleep disorders into those that happen during REM (Rapid Eye Movement) and those that occur during non-REM."
REM and non-REM are stages of the typical sleep cycle.
"Dreaming and nightmares occur during REM, while true night terrors occur in non-REM," he said. "If you wake someone up when they're dreaming, they can tell you what they were dreaming about. If you wake them up during night terrors, they'll feel awful, but they won't know why.
"The phase of non-REM sleep in which night terrors and sleepwalking typically occur is called N3."
Because young children spend a lot of sleep time in N3, they are also those most likely to suffer night terrors and sleepwalking bouts.
"People don't like to wake sleepwalkers because they sometimes come out of it in a confusional state," Coats said. "For the most part, it's not dangerous to wake a sleepwalker. It is, though, probably necessary some of the time. Adult sleepwalkers who leave their homes can hurt themselves badly. If it's a child, it's usually not such a big deal, since kids are less likely to leave the house - not to mention drive."
Coats recommends an inexpensive door alarm or simple bell to notify others in the house when someone may be sleepwalking.
The Mayo Clinic said that up to 15 percent of children sleepwalk, while a Stanford University study found that 3.6 percent of adults report sleepwalking.
The incidence of night terrors in both children and adults is relatively rare.
What causes sleepwalking?
"We don't know why some people sleepwalk and some people don't," Coats said. "In kids, it's common for them to have a parent who's a sleepwalker. The majority of children, however, do outgrow it over time."