Déjà vu is defined as a moment during which you have already seen or experienced something that, in actuality, you have never experienced. Déjà vu has happened to all of us. We are intimately familiar with a conversation with a group of friends that we’ve never had before, like we are watching ourselves talk from a place outside of our bodies. We travel to a remote Buddhist temple in Thailand and are certain that we were there before.

This phenomenon is not reserved for people who believe in reincarnation, but it certainly must be tied to this belief system. Why would something you’d never seen before seem so familiar? Why would something that had never happened to you before seem like you’re replaying a scene from a movie?

Most people, around 70 percent of the population, have reported experiencing déjà vu at some point in their lives. Perhaps surprising, however, 15 to 25 year-olds report experiencing the greatest number of déjà vu instances. It seems that older people would draw more correlations between seemingly unrelated occurrences simply because they have a greater well of experiences.

Turns out, there are two types of déjà vu. Swiss scholar Arthur Funkhouser argues that déjà experiences should be grouped into two distinct categories and given two different names: déjà visite (“already visited”) if you recognized a place that you had never been or déjà veca (“already experienced or lived through”) if you remembered an experience that you never had.  

Weirder yet, the explanation for the experience. Scientists say that the sensation of déjà vu is associated with temporal-lope epilepsy, specifically right before a temporal-lobe seizure. Déjà vu either occurs right before the seizure or during it.

Constant occurrences of déjà vu doesn’t mean that you’re unwell in the head or that you need to go to the doctor, though. However, some people with brain injuries or other medical conditions do experience déjà vu, as well.

Psychoanalyst and psychiatrists are still out on the cause and correlation of déjà vu. Some psychoanalysts say that the phenomenon is related to wish fulfillment or fantasy. Psychiatrists say that it could be related to some mismatching in the brain that causes it to temporarily mistake the present for the past.

Whatever the cause, it seems that the verdict on the real necessity and circumstances of déjà vu is still out.

Do you experience déjà vu? Do you think of it as a good or bad experience?