The most disturbing thing about exploding head syndrome is when it hits you. Just in the process of drifting off to sleep, people suddenly think they hear a piercing, crashing noise.
“It’s usually very short, very loud — like a gunshot or explosion,” says Dan Denis, a psychologist with the University of York in the U.K. “It can be pretty scary.”
Many people have experienced this once in their life, and a smaller subset reported recurrent episodes, sometimes as much as once per month. Exploding head syndrome happens between unconsciousness and consciousness and is a sensation that’s intertwined with other sensations. Scientists are just learning more about it, but here’s what they know so far.
