Déjà vu is a French term that literally means "already seen" and is reported to occur in 60-70% of people, most commonly between the ages of 15 and 25. The fact that déjà vu occurs so randomly and rapidly—and in individuals without a medical condition—makes it difficult to study, and why and how the phenomenon occurs is up to much speculation.
A related ...
There are very few research data available on the efficacy
of hypnosis in the treatment of sleep disorders. Most of the
literature is limited to case reports or studies with such a
small sample that at times it is very difficult to interpret the
results. There is a major placebo effect, so uncontrolled
trials are of limited value.