Whether we admit it or not, we’ve all thought about ghosts at some point. But what makes us feel in the presence of spirits?

Sleep paralysis – Although doctors don’t yet know exactly how this phenomenon occurs, it’s thought to be part of REM sleep, during which you can have dreams that seem real. They suffer from sleep paralysis, feel as if someone is pressing down on them or have hallucinations. Sometimes he feels as if someone has entered his room, sometimes as if something is hovering over his bed.

Mold – It may seem strange, but scientists have linked air quality to ghost sightings. As it turns out, toxic mold spores can cause mood swings, irrational anger, and even brain damage if you’re exposed for too long.

Exploding Head Syndrome – This may sound like a made-up condition, but it’s actually a very real and scary sensory disorder. According to Goldsmiths University, it is characterized by “the perception of a loud noise or the sensation of an explosion in the head, usually when transitioning from deep sleep to wakefulness. Two years ago, a study found that 44.4 percent of people experienced significant fear during these episodes, with a small proportion believing it was caused by something supernatural.

Carbon Monoxide – Links between carbon monoxide and paranormal experiences have been considered since before World War II. In 1921, the American Journal of Ophthalmology recounted the chilling experience of a woman known only as “Ms. H.” After moving into a new house, she and her family started hearing strange voices and even felt like they had other people in their beds. This was accompanied by feeling weak and suffering from a headache, which actually turned out to be the result of carbon monoxide poisoning. This toxic gas (CO) is a tasteless and odorless menace that, even at low concentrations, can cause harm to humans who inhale it. It often comes from burning fuels like gas and propane, as well as wood-burning fireplaces and blocked chimneys.

Pareidolia – If you’ve thought you saw something scary in the bushes, chances are you’ve experienced what’s called pareidolia. This is the same phenomenon that happens when you see people’s faces through the clouds.