Quartz recently released a fascinating video that looks at the question, “Why are people everywhere having the same nightmare?” Specifically, the dream involves a scary-looking guy in a large hat.

The reporter, Corrinne Purtill, found dozens of accounts of people seeing “Hat Man” just before periods of terrifying sleep paralysis. It all sounds very strange—and very creepy.

However, the explanation seems to be more scientific than purely supernatural. As it turns out, throughout recorded history, people have had a nightmare where some figure—like the Hat Man—appears to be pushing on their chest, paralyzing them while they attempt to wake from their sleep.

Thanks to modern sleep science, there is a medical explanation. Sleep paralysis involves the brain waking before the body, and it is relatively normal. It’s not uncommon for people to have hallucinations in this state while the mind tries to figure out what is going on.

So, why are people all dreaming about Hat Man?

One expert Quartz spoke to says images in our subconscious are often affected by cultural influences. For many people, the image of horror movie villain Freddy Krueger has become so synonymous with nighttime terror it isn’t that surprising the mind thinks of him when it is experiencing something like sleep paralysis, which it doesn’t fully understand.