Alien abduction stories have been circulating for decades. The classic version includes someone being sucked up by a beam of light in the middle of the night, and weird-looking green creatures subject that person to horrifying experiments, like the dreaded anal probe.

How much truth is there to these stories? We can’t say for sure, especially since anal probes bear a striking resemblance to the cameras shoved up our butts on tubes during a colonoscopy. But scientists have some explanations for why people tell mysterious tales about alien abductions or UFO sightings.

Read: Can You Be Buried Alive?

According to The Conversation, some “fantasy-prone people engage in elaborate imaginings and often confuse fantasy with reality” — they may appear well-adjusted, but they are combining real events with imagined ones. In cases of great stress, those people may also experience dissociation, in which people feel detached from reality.

Being trapped in a place between sleeping and wakefulness could also lead to someone believing they’ve been abducted by aliens. When a person wakes up before their sleep cycle is finished, they could experience sleep paralysis, in which their mind is still in a dreaming state and their muscles cannot move but they are conscious. “This can be an exceptionally scary time for those afflicted with this weird phenomenon, but despite former beliefs, the feeling of paralysis is not caused by supernatural beings,” Live Science says.

And The Conversation says the symptoms of sleep paralysis line up with how many people describe their alien abduction: “a sense of being awake, not dreaming, and realistic perceptions of the environment.”

“The inability to move, a feeling of fear or dread, and the sense of another presence — perhaps evil or malevolent — are common symptoms,” that publication says. “Also common are a feeling of pressure on the chest and difficulty breathing, and of being held or restricted to a lying position: most sleep paralysis attacks occur while the individual is lying on their back.”

So the next time you think you’ve been abducted by aliens, don’t jump to conclusions; there may be an alternate explanation.

R.I.P. Russell Casse, American hero Independence Day

See also:

What Drowning Feels Like

4 Gruesome Ways to Die at Home

How Fire Actually Kills You