What can explain that eerie, unsettling feeling we sometimes get that we've experienced a new situation once before?
It might just be the weirdest experience you'll ever have sober, but what exactly is deja vu?
One thing it definitely is, is common.
Two-thirds of us have had it, with younger people, globetrotters, and film fans likely to get it more frequently.
Because of its inherent weirdness, deja vu was long thought of alongside paranormal events like clairvoyance and reincarnation.
In fact, it was parapsychologist Émile Boirac who first named the feeling in the 1870s using the French for "already seen."
The focus on the uncanny has persisted, and in films like "The Matrix," deja vu is a glitch in the computer simulation.
So, what's actually going on?
The truth is, no one is 100 percent sure, but psychologists have suggested dozens of possibilities combining theories of memory, perception, and cognition.
One is divided perception.