If you have ever there was a clear sense that a new event (or situation) has happened(a) in the past, you have experienced "deja vu". Sometimes it seems that the event (situation) were you have lived in a dream. This feeling is associated with disorder of the functions of the brain, and past life.
Deja vu is the feeling that you were a witness or participant of the current situation once before. In other words, you think your "right now" has been in the past. I tend to view the flashback as a memory o the future. About the part that's happening right now. Experiencing deja vu, you know what will happen in a second or a few seconds. Usually this feeling lasts for 5-10 seconds. You think you have either been in the same situation or just know what's about to happen.
Scientists have found that the feeling may occur due to improper functioning of the brain (disruption of memory processes). Some medications (amantadine and phenylpropanolamine) are also considered as cause of the phenomenon. These drugs cause disturbances in areas of the brain responsible for long term memory.
The human brain is complex and amazing organ. The brain creates associations between different situations. The brain often tries to experimentally reproduce a situation that he never before experienced. Therefore, the expectation of a certain event can cause a person to think that he has already participated in a similar event in the past.