Sometimes I experience instances in my life which I THINK I have encountered or experienced before, usually because the sights and/or sounds of the "déjà vu moment" are familiar, or make me feel as if it is in my memory somewhere as the exact same sequence has occurred before.
How can these "déjà vu instances" be explained? Is there a simple cognitive explanation behind this, or is it physics-related (i.e. belief in a parallel universe or some other theory that the future has actually happened already)?
I realize that many of my friends also experience this same kind of thing. Is it therefore a phenomenon that every human being will encounter?
Has this question been asked before...?!? Just kidding. Déjà vu, that mistaken feeling that you've been somewhere or seen something before, has intrigued people for centuries, yet it is still not well-understood. The term déjà vu literally translates to "already seen," and as many as 80 percent of people report having had at least one experience of déjà vu in their lifetime. You, your friends, and Yogi Berra (who coined the redundant, but clever phrase, "it's like déjà vu all over again!") are certainly not alone with this mysterious trick your brain plays on you. While mystifying, déjà vu can be mostly boiled down to two main types: ictal déjà vu, which is an often unpleasant and intense version associated with a seizure disorder called epilepsy, and physiological déjà vu, which is that strange, yet fleeting feeling that non-epileptic folks experience. Younger people are most likely to have one of these creepy, been-there-done-that moments, but all sorts of people report the experience of déjà vu. In fact, déjà vu might not be too distant from dreams or hallucinations — all of these semi-surreal moments may be due, in part, to your brain's effort to untangle all the stimuli coming at it.
The general consensus is that it’s a cognitive sensation, not related to physics or a parallel universe. Theorists suggest it may be caused by issues with memory retrieval or delayed neurological responses. Exactly which brain processes or structures are at play in déjà vu isn't totally clear to researchers yet, but research among epileptic patients has given some hints. It seems that ictal déjà vu might have something to do with the temporal lobe of the brain. Those with ictal déjà vu often have unpleasant symptoms along with their experiences, which can include feeling fearful, having headaches, or fatigue. Ictal episodes in those with epilepsy also usually last longer (up to a couple minutes) than physiological déjà vu episodes in non-epileptic folks (which usually last just a few seconds). Among non-epileptic people, the limbic system (a section of the brain partially responsible for long-term memory and emotions) is thought to be a major player.
Perhaps you've experienced other more familiar mind-bending phenomena before that can help you feel more comfortable the next time you're having a déjà vu moment. Dreams and hallucinations are probably the most common relatives of déjà vu, which are part of a loosely-knit family called "reality-testing" experiences. Less common reality-testing experiences include "déjà vécu" (false recollections of specific memories of things that never actually happened) and "jamais vu" (experiencing something familiar that in the moment feels unfamiliar and strange). Basically, your brain is a hard-working machine that's continually processing all sorts of sensory inputs and memories trying to make sense of this crazy world. Just like any other machine, the wires might get crossed in the process at times and under certain conditions.
That said, if your health or safety is ever compromised during a déjà vu episode, dream, hallucination, or other surreal experience, consider seeking the advice of a health care provider. As mentioned, seizures are one common cause of déjà vu, and seizure disorders can be serious if left untreated. Excessive drug or alcohol use could also be behind mental mix-ups and could pose serious risks to your health. Do your episodes bother you emotionally or are they impeding your everyday life? If so, a mental health professional may be able to help sort out any appropriate treatment or management strategies.
If your déjà vu is just an occasional funny moment, though, then you likely need not worry too much. Perhaps you can just be grateful that you're not living your own personal Groundhog Day, where déjà vu lasts years rather than seconds — eek!Alice!