A brain phenomena called "sleep paralysis" helps to explain why some people report having memories of being abducted by aliens.
When we dream, our brain shuts off our ability to move so that we don't injure ourselves, acting out those dreams, National Geographic reports. When we wake up, it switches our ability to move back on again. Sometimes the switch is out of sync and we wake up, paralyzed.
Brian Sharpless, a clinical psychologist at Penn State, specializes in studying sleep paralysis. He says that sleep paralysis can be a terrifying experience, not only for the paralysis but for the hallucinations that often accompany it. The hallucinations vary, but come in three general types: the intruder, the incubus — something pressing on your chest, and levitation. Put them together and you might have something strikingly similar to a UFO abduction story. "I think all three categories are consistent with what people who report being abducted by aliens experience — having a presence in the room, the feeling that someone's on top of you, sexually assaulting you, or potentially levitating you," Sharpless says.
Sleep paralysis has happened to people throughout the ages, and hallucinations are reflective of the culture . "Where one time or place might find witches, demons, ghosts and spirits as an explanation for sleep paralysis, it's possible that 21st century Americans might find technologically advanced aliens as an explanation."