Sleep paralysis is a little known but real brain phenomenon where folks experience a waking nightmare with evil goblins entering their room, siting on their chest, uttering threats and inhibiting their breathing.

Sleep paralysis embodies a universal, biologically based explanation for pervasive beliefs in spirits and supernatural beings, even in the United States, Hufford argues. The experience thrusts mentally healthy people into a bizarre, alternative world that they frequently find difficult to chalk up to a temporary brain glitch.

Many who experience sleep paralysis also report sensations of floating, flying, falling, or leaving one's body.

Two brain systems contribute to sleep paralysis, Cheyne proposes. The most prominent one consists of inner-brain structures that monitor one's surroundings for threats and launches responses to perceived dangers. As Cheyne sees it, REM-based activation of this system, in the absence of any real threat, triggers a sense of an ominous entity lurking nearby. Other neural areas that contribute to REM-dream imagery could draw on personal and cultural knowledge to flesh out the evil presence.

A second brain system, which includes sensory and motor parts of the brain's outer layer, distinguishes one's own body and self from those of other creatures. When REM activity prods this system, a person experiences sensations of floating, flying, falling, leaving one's body, and other types of movement.

The article describes how cultural influences affect those experiencing SP, Cambodian refugees, African Americans, etc. What's really interesting is that this scientifically researched phenomema may help explain those ludicrous tales of alien abductions. The victims aren't really the gullible fools they seem to be but just folks experiencing sleep paralysis influenced by their UFO 'culture'.

Accounts of space-alien encounters typically begin with the abductee waking in the night while lying face up, McNally says. The person can't move but senses electric vibrations. A feeling of terror makes breathing difficult. Alien beings advance to the foot of the bed or climb on top of the person, who then experiences a sense of floating or of being transported to an alien craft.

Days or weeks later, in response to a therapist's hypnotic suggestions, the abductee may generate details of being sexually probed or otherwise assaulted by the aliens, McNally notes.

Claims of abductions by space aliens trigger much controversy, media attention, and ridicule. The late Harvard psychiatrist John Mack fueled the hubbub by defending the accounts as descriptions of actual encounters with visitors from other planets.

There's another, far more likely, explanation for the reported experiences of the "abductees," says McNally. Traumatic encounters that a person seems to experience during sleep paralysis feel as vividly real as anything that happens during the day does, he notes.

Despite their fantastic claims, these people are mentally healthy, says McNally.

McNally and Clancy linked the claims of 10 alien abductees to episodes of sleep paralysis.

Even the most rational people who experience sleep paralysis often find it difficult to write off their nighttime ordeals as unreal, Hufford notes. He has interviewed many U.S. medical students who, even after hearing about REM sleep and the brain's threat-detection system, insist that their frightening meetings with the Night Crusher were real. Until sharing their stories with Hufford, most of the students had never told them to anyone.