You jerk awake in the middle of the night in confusion. Is there a figure standing in the corner of the room? Your brain begs your limbs to move, but nothing happens. The anxiety increases. Your eyes scan the room. Just as you're about to hit peak panic, you sit up and the figure disappears.
You've just experienced sleep paralysis, one of many "parasomnias," which is the name experts give to all sorts of weird things that occur during sleep.
Sleep paralysis happens when the brain incapacitates the body to prevent it from acting out the vivid dreams occurring during REM (or, rapid eye movement) sleep. It often comes with a feeling of immobility, and a sense of choking.
The good news is, it's absolutely normal. Even if it's terrifying.
But when sleep paralysis happens outside of deep sleep — when a person is just dozing off or waking up — it can be "disruptive of the architecture of sleep," said Baland Jalal, a researcher who investigates the phenomenon. That could lead to more sleep paralysis. People with poor sleeping habits experience the phenomenon more frequently.
While the mechanisms behind sleep paralysis remain murky, Jalal said stress and worry play a part. Recent research indicates that people with anxiety and PTSD report experiencing sleep paralysis more frequently.
"People who are anxious have much more emotional sleep. [They] are more likely to wake up during REM," said Jalal. "If you have sleep paralysis, you probably also have anxiety."
The anxiety feeds into the sleep paralysis, said Jalal. People fret about experiencing the panicky feelings of sleep paralysis, which makes it more likely to occur again.
While about 6 percent of the population will experience sleep paralysis at one point in their lives, it occurs in about 30 to 50 percent of people with narcolepsy, a sleep disorder that includes excessive daytime sleepiness, cataplexy, sleep paralysis, and hallucinations, said Dr. Nathaniel Watson, president of the American Academy of Sleep Medicine and co-director of the University of Washington Medical Sleep Center.
Students are more likely to experience sleep paralysis with as many as 28.3 percent of students reporting it.
Some people report the feeling that someone or something is trying to strangle or choke them or will see someone coming into their room and not able to move or scream, experts say. It can also happen when the person is awake, lasting from a few seconds to a minute or two. It's associated with hypnagogic hallucinations, which occur as a person is falling asleep.
For most people, "it is not indicative of any kind of disease," said Watson. While the experience feels frightening, the episodes last only a few seconds or minutes at most.
Most people slip out of it as quickly as they fell into it. A light touch from a partner can be enough to stop it, he said.
While not everyone who has sleep paralysis experiences hallucinations, seeing a person or a ghost in the room is the most common vision, said Jalal.
Hallucinations vary by culture — the Chinese call it "guiya" or ghost pressure because they believe a ghost sits on people's chests. In Newfoundland, it is the "old hag" because people see a witch and in Egypt people see Jinn (what Westerns call genies), which are known to hunt and sometimes kills their victims.
These ghostly "waking dreams” can involve serpents, spiders, intruders and even ghosts. They're often associated with feelings of dread.
Some experts have suggested that alien abductions are really just intense bouts of sleep paralysis.
"When you live in a culture where you are afraid of it, you are much more likely to be anxious [about sleep paralysis] and experience it," Jalal said.
Sometimes an environmental reason is the cause of the spectral vision.
In 2005, the Journal of Emergency Medicine reported about a 23-year-old woman who was found delirious and hyperventilating after seeing a "ghost".
"On arrival in the ED (about 30 minutes later), the patient was still hyperventilating but was able to talk. She denied taking illicit drugs or alcohol but recalled seeing a ghost while taking bath," the researchers wrote.
It was later determined that her new gas water heater had been improperly installed and her house was filled with carbon monoxide. After oxygen therapy, she made a full recovery.