39 Unnerving Encounters That People Say Will Stay With Them Forever

"I see dead people..."

It's a line from a movie that you're unlikely to forget if you ever watched it from the edge of your seat. The 1999 horror/mystery The Sixth Sense centers around a little boy haunted by a dark secret: ghosts come to visit him and speak to him about their problems. The terrified child confides in a psychologist who tries to make sense of his supernatural abilities, with some unexpected consequences for both of them.

The movie might be fictional, but many people claim to 'see dead people' in real life. In fact, around 18% of Americans swear they've encountered a ghost at least once according to a Pew Research Center survey. If you've never had the pleasure - or displeasure - of meeting Casper and his friends, you might be wondering why.

Psychologists say it has to do with your beliefs, your personality and your religious background.

“The first requirement for there being a ghost in the house is someone believing there’s a ghost in the house,” said a wise man once. His name is Christopher Bader and he is a Professor of Sociology at Chapman University. He also wrote a book called “Paranormal America: Ghost Encounters, UFO Sightings, Bigfoot Hunts, and Other Curiosities in Religion and Culture.”

Basically, what Bader meant is that you have to believe in the paranormal to be able to 'see' a ghost. "Our perception of what is going on around us at any given moment is driven by our expectations, needs, and beliefs, and this is especially true when the sensory information we are receiving is sketchy and ambiguous," explain the experts over at Psychology Today.

Bader says more than half of Americans (52% and rising) admit to having a paranormal belief or experience. And this isn't always to do with seeing spirits or ghosts.

"Some believers in the paranormal search the skies for unexplained lights, go on late-night hunts for ghosts or hike through North American woods in search of Bigfoot," notes the Chapman University site. "Some believe in the lost city of Atlantis, demon possession, prophetic dreams, reiki, healing sounds, power crystals and tarot cards."

Bader surveyed 4,000 Americans. His research found that a quarter of them have read or researched the world of ghosts, hauntings and apparitions.

Interestingly, "men are more likely to connect with the paranormal via cryptozoology, or animals of folklore (Bigfoot, the Loch Ness Monster, the Chupacabra)," notes the uni site, while "women are more drawn to New Age connections (psychics, mediums, astrology, ghost contact)."

Further research shows that people who believe in the paranormal are more likely to embrace conspiracy theories and pseudoscience. Psychology Today notes that a history of childhood trauma has also been linked to paranormal beliefs. You're also more likely to "see ghosts" if you are an intuitive thinker, as opposed to an analytic one.

Chris French is the head of the Anomalistic Psychology Research Unit at Goldsmiths, University of London. The self-proclaimed skeptic says he doesn't believe that paranormal forces exist, but is always open to being proven wrong.

French defines anomalistic psychology as being focused upon "trying to come up with, and where possible put to the test, non-paranormal explanations, usually psychological explanations, for ostensibly paranormal experiences."

So what does he make of people who claim to get ghost visitors in the dead of the night?

According to French, a phenomenon called “sleep paralysis” can play a part. It's basically a hybrid state between normal waking consciousness and dream consciousness. Think of it as half awake but half asleep, unable to move, and temporarily paralyzed.

French says while sleep paralysis is fairly common in its most basic form, some people get very vivid hallucinations while they're going through it and lying in bed. You can get a host of associated symptoms, he explains.

"You can get a sense of presence, feeling that there's something evil in the room with you, even if you can't see it or hear it, you just know it's there. But sometimes people do actually hallucinate. So they might hear voices or footsteps or mechanical sounds, they might see lights moving around the room or dark shadows or even demons, witches, all sorts of stuff," French said, adding that often, people report a sense of pressure on the chest, and difficulty breathing.

"And if you already believe in ghosts or demons and so on, it's not surprising that they will sometimes opt for that as an explanation," he explained.

So what's the expert's message to those who claim to believe in the paranormal?

For one, he says he'd advise them to base their beliefs about the way the universe operates on "solid empirical evidence, preferably from well-controlled studies," rather than personal experience.

However, he adds that science is not an established body of facts, it's something that evolves. Scientists will sometimes change their minds on issues, he says, and that's a good thing.

"It's a pity we don't have more politicians who are able to do that... That's how we've ended up with Brexit and maybe how you ended up with Trump," French said during a podcast. The skeptic added that he has great respect for people who stand up and say, “Actually, I realized I was wrong about that.”