Maybe this has happened to you: You’re visiting someplace for the first time. And although you know you’ve never been there before, you could swear that the place looks familiar. The strange feeling of disorientation—fleeting, lasting less than 30 seconds—makes you uneasy. Is your mind playing tricks on you?Actually, you’ve just experienced déjà vu.Don’t worry—you’re in good company. Most American adults (about two out of three, in fact) report having had moments of déjà vu, which Southern Methodist University psychology professor Alan S. Brown, Ph.D., defines as “an experience where you have a very strong sense of familiarity in the face of an objectively new experience.”MORE: How to Lucid DreamDéjà vu can take many forms. “The term déjà vu actually means ‘already seen,’ says Anne M. Cleary, Ph.D., associate professor in the Cognitive Psychology Program at Colorado State University, “though people today use the term more broadly to mean ‘already experienced.’ There are many other ‘déjàs’ however. For example, déjà sentí is the feeling of having smelled something before, déjà gouté is the feeling of having tasted something before, déjà lu is the feeling of having read something before, déjà parlé is the feeling of having spoken something before and déjà pensé is the feeling of having thought something before.”A Brief Brain HiccupBrown and Cleary, who are leading researchers of the phenomenon, explain that no one completely understands déjà vu and in fact, scientists have proposed over 40 possible causes for it.“Several theories suggest it might be a small seizure in that area of the brain that handles memory and familiarity,” says Brown. “Also, it may be because different neurological pathways in the brain that normally work together in a seamless fashion momentarily get out of sync with each other; sort of a brief brain hiccup,” he explains. When that happens, you think the same thought twice without knowing it. And the milliseconds between those two thoughts can give you the feeling of glimpsing into your distant past.What Makes a Déjà Vu-er?  In order to experience déjà vu, you have to be prone to it. Déjà vu-ers tend to be people who are educated and liberal. They are open to new and different experiences and willing to accept rather than dismiss them. They’re also frequent travelers, readers or movie-watchers, and they remember their dreams. They have built up a very large stockpile of images and experiences that feed the déjà vu reaction.Interestingly, young people report experiencing déjà vu more often than older adults. “This is a curious finding,” says Brown, “because cognitive difficulties tend to increase with age, not decrease. We are still trying to figure it out, but it may be that older adults are used strange cognitive experiences happening to them (odd familiarity experiences, or strange memory lapses). They get more accustomed to such memory glitches as routine, and are less likely to notice them or remember them.”Not only do you have to be prone to experiencing déjà vu, but the circumstances also must be right. You’ll probably sense it more often in the evening, on the weekend, when you’re fatigued, under stress, doing everyday tasks or relaxing. Déjà vu can happen when your mind is momentarily distracted from what you’re looking at so that you don’t perceive it completely the first time around.QUIZ: Measure Your Life SatisfactionTriggering Déjà VuSuppose you and your circumstances are ripe for the déjà vu experience, what actually triggers it? According to Cleary, familiarity and recognition are the keys. First, something happening to you at the moment must strike you as familiar (an object, a face, a bit of architecture or even an entire setting), and you recognize that it’s familiar.For example, you might see in a hotel lobby the same kind of lamp your parents had when you were a child. Or part of the layout of a new friend’s apartment may be just like your old college dorm room. These elements can trigger the temporary disorienting feeling of déjà vu.Other than that unsettling feeing of doing something before, is there any benefit to experiencing déjà vu? Cleary seems to think so. She believes that the sensation can serve as a kind of prompt to alert you to a particular, untapped memory—one that merits some more mental digging. Déjà vu might also help with decision-making. “If something feels familiar that alone may be telling us something important about the situation that should give us pause before proceeding.”And that’s something you may want to remember.MORE: How Does Your Memory Work?