Déjà vu is a bit of a mystery. Experts aren’t sure what causes the sensation of having experienced something before, but they have some compelling theories.

“Déjà vu” describes the uncanny sensation that you’ve already experienced something, even when you know you never have.

Say you go paddleboarding for the first time. You’ve never done anything like it, but you suddenly have a distinct memory of making the same arm motions, under the same blue sky, with the same waves lapping at your feet.

Or perhaps you’re exploring a new city for the first time and all at once feel as if you’ve walked down that exact tree-lined footpath before.

You might feel a little disoriented and wonder what’s going on, especially if you’re experiencing déjà vu for the first time.

It’s often nothing to worry about. Although déjà vu can accompany seizures in people with temporal lobe epilepsy, it also occurs in people without any health issues.

There’s no conclusive evidence on how common it actually is, but varying estimates suggest anywhere between 60 and 80 percent of the population experience this phenomenon.

While déjà vu is fairly common, especially among young adults, experts haven’t identified a single cause. (It’s probably not a glitch in the Matrix.)

Experts do, however, have a few theories about the most likely underlying causes.

Researchers can’t easily study déjà vu, partially because it happens without warning and often in people without underlying health concerns that might play a part.

What’s more, déjà vu experiences tend to end as quickly as they begin. The sensation may be so fleeting that if you don’t know much about déjà vu, you may not even realize what just happened.

You might feel a bit unsettled but quickly brush off the experience.

Experts suggest several different causes of déjà vu. Most agree it likely relates to memory in some way. Below are some of the more widely accepted theories.

Split perception

The theory of split perception suggests déjà vu happens when you see something two different times.

The first time you see something, you might take it in out of the corner of your eye or while distracted.

Your brain can begin forming a memory of what you see even with the limited amount of information you get from a brief, incomplete glance. So, you might actually take in more than you realize.

If your first view of something, like the view from a hillside, didn’t involve your complete attention, you might believe you’re seeing it for the first time.

But your brain recalls the previous perception, even if you didn’t have total awareness of what you were observing. So, you experience déjà vu.

In other words, since you didn’t give the experience your full attention the first time it entered your perception, it feels like two different events. But it’s really just one continued perception of the same event.

Minor brain circuit malfunctions

Another theory suggests déjà vu happens when your brain “glitches,” so to speak, and experiences a brief electrical malfunction — similar to what happens during an epileptic seizure.

In other words, it can happen as a sort of mix-up when the part of your brain that tracks present events and the part of your brain that recalls memories are both active.

Your brain falsely perceives what’s happening in the present as a memory, or something that already happened.

This type of brain dysfunction generally isn’t cause for concern unless it happens regularly.

Some experts believe another type of brain malfunction may cause déjà vu.

When your brain absorbs information, it generally follows a specific path from short-term memory storage to long-term memory storage. The theory suggests that, sometimes, short-term memories can take a shortcut to long-term memory storage.

This can make you feel as if you’re retrieving a long-ago memory rather than something that happened in the last second.

Another theory offers the explanation of delayed processing.

You observe something, but the information you take in through your senses is transmitted to your brain along two separate routes.

One of these routes gets the information to your brain a little more rapidly than the other. This delay may be extremely insignificant, as measurable time goes, but it still leads your brain to read this single event as two different experiences.

Memory recall

Many experts believe déjà vu has to do with the way you process and recall memories.

Research conducted by Anne Cleary, a déjà vu researcher and psychology professor at Colorado State University, has helped generate some support for this theory.

Through her work, she’s found evidence to suggest déjà vu can happen in response to an event that resembles something you’ve experienced but don’t remember.

Maybe it happened in childhood, or you can’t recall it for some other reason.

Even though you can’t access that memory, your brain still knows you’ve been in a similar situation.

This process of implicit memory leads to the somewhat odd feeling of familiarity. If you could recall the similar memory, you’d be able to link the two and likely wouldn’t experience déjà vu at all.

This commonly happens, according to Cleary, when you see a particular scene, like the inside of a building or a natural panorama, that’s very similar to one you don’t remember.

She used this finding to explore the idea of premonition associated with déjà vu in a 2018 study.

You may have experienced this yourself. Many people report that déjà vu experiences trigger a strong conviction of knowing what’s going to happen next.

But Cleary’s research suggests that even if you feel certain you can predict what you’re about to see or experience, you generally can’t.

Further research may help better explain this prediction phenomenon, and déjà vu in general.

This theory rests on the idea that people tend to experience feelings of familiarity when they encounter a scene that shares similarities with something they’ve seen before.

Here’s an example of Gestalt familiarity: It’s your first day at a new job. As you walk into your office, you’re immediately taken aback by the overwhelming feeling you’ve been here before.

The reddish wood of the desk, the scenic calendar on the wall, the plant in the corner, the light spilling in from the window — it all feels incredibly familiar to you.

If you’ve ever walked into a room with a similar layout and placement of furniture, chances are good you’re experiencing déjà vu because you have some memory of that room but can’t quite place it.

Instead, you just feel as if you’ve seen the new office already, even though you haven’t.

Cleary also explored this theory. Her research suggests people do seem to experience déjà vu more often when viewing scenes similar to things they’ve already seen but don’t remember.

A collection of other explanations for déjà vu also exist.

These include the belief that déjà vu relates to some kind of psychic experience, such as remembering something you’ve experienced in a previous life or in a dream.

Keeping an open mind is never a bad thing, but there’s no evidence to support either of these ideas.

Different cultures may describe the experience in various ways, too.

As “déjà vu” is French for “already seen,” the authors of one 2015 study wondered whether the French experience of the phenomenon would differ, since people who speak French could also use the term to describe a more concrete experience of seeing something before.

Their findings didn’t shed any light on potential causes of déjà vu, but they did find evidence to suggest the French study participants tended to find déjà vu more disturbing than English-speaking participants.

Déjà vu often has no serious cause, but it can happen just before or during epileptic seizures.

Many people who experience seizures, or their loved ones, realize what’s happening pretty quickly.

But focal seizures, while common, aren’t always immediately recognizable as seizures.

Focal seizures start in just one part of your brain, though it’s possible for them to spread. They’re also very short. They can last for a minute or two, but they could end after only a few seconds.

You won’t lose consciousness and might have complete awareness of your surroundings. But you might not be able to react or respond, so other people might assume you’re zoning out or staring off into space, lost in thought.

Déjà vu commonly happens before a focal seizure. You might also experience other symptoms, such as:

  • twitching or loss of muscle control
  • sensory disruptions or hallucinations, including tasting, smelling, hearing, or seeing things that aren’t there
  • repeated involuntary movements, like blinking or grunting
  • a rush of emotion you can’t explain

If you’ve experienced any of these symptoms, or regularly experience déjà vu (more than once a month), it’s generally a good idea to see a healthcare provider to rule out any underlying causes.

Déjà vu can be one symptom of dementia. Some people living with dementia may even create false recollections in response to repeated experiences of déjà vu.

Dementia is serious, so it’s best to talk to a healthcare provider about any symptoms in yourself or a loved one right away.

Déjà vu describes that uncanny sensation you’ve already experienced something, even when you know you never have.

Experts generally agree this phenomenon probably relates to memory in some way. So, if you have déjà vu, you might have experienced a similar event before. You just can’t remember it.

If it only happens once in a while, you probably don’t need to worry about it (even though it can feel a little strange). But you could notice it more if you’re tired or under a lot of stress.

If it’s become somewhat of a regular experience for you, and you don’t have seizure-related symptoms, taking steps to relieve stress and get more rest may help.

Crystal Raypole has previously worked as a writer and editor for GoodTherapy. Her fields of interest include Asian languages and literature, Japanese translation, cooking, natural sciences, sex positivity, and mental health. In particular, she’s committed to helping decrease stigma around mental health issues.