We all know that "Déjà vu" is the experience of being certain that you have experienced or seen a new situation previously – you feel as though the event has already happened or is repeating itself. The experience is usually accompanied by a strong sense of familiarity and a sense of eeriness, strangeness, or weirdness. The “previous” experience is usually attributed to a dream, but sometimes there is a firm sense that it has truly occurred in the past.
Some people may claim that this phenomenon is caused due to the fact that we have lived another life before or even that we relive the same life over and over again. This might explain why we have this sense of familiarity at certain moments in our lives.
"Jamais vu" (never seen) on the other hand, describes a familiar situation which is not recognized. It is often considered to be the opposite of déjà vu and it involves a sense of eeriness. The observer does not recognize the situation despite knowing rationally that they have been there before. It is commonly explained as when a person momentarily doesn’t recognize a person, word, or place that they know. Chris Moulin, of Leeds University, asked 92 volunteers to write out “door” 30 times in 60 seconds. He reported that 68 per cent of his guinea pigs showed symptoms of jamais vu, such as beginning to doubt that “door” was a real word. This has lead him to believe that jamais vu may be a symptom of brain fatigue.