Déjà vu in Islam
Question

Can you please tell if there is an Islamic explanation of Deja vu (seeing something and realizing that you have seen the exact same thing before). What should a person do when such a thing happens to him?
Praise be to Allah.Déjà vu is a French phrase meaning already seen. It refers to a person feeling that he has lived or seen a thing before the situation he is currently experiencing occured.
Neurologists and psychologists differed concerning the explanation of this phenomenon.
Some of them attribute Déjà vu to an anomaly in the memory, having to do with connections between the nerves that are responsible for the short-term memory and the long-term memory.
Some of them attribute it to feelings or emotions being experienced in the present, that bring to mind details of some past events, which makes us feel that we have lived the present event before.
Some of them attribute it to information that we learned before, but we forgot it, then the brain retrieved it, so we imagine that we lived through the event twice.
However, many religious beliefs and parapsychological schools of thought attribute the phenomenon of déjà vu to supernatural forces, or parapsychological interpretations, explaining it on the basis of ideas such as telepathy or hypnosis, or attributing it to ghosts or poltergeists, or other speculative interpretations for which there is no evidence.
You should understand that there is no Islamic explanation for this phenomenon, and it is not discussed in the Quran or the Sunnah, or by any of the scholars of Islam, and it has no connection to any of the fundamental or basic teachings of Islam.
Regarding this matter, there is nothing except hypothesis or observation in the realms of experimental neurology, or speculation and claims made by followers of innovated or polytheistic religious beliefs that have nothing to do with Islam.
If this happens to you, all you have to do is reflect on the great blessing that Allah has bestowed upon you by maintaining your memory and keeping it free from troubles and ailments, and protecting your mind from mental illness and harm. How confused have the scientists been, and how much have they argued and differed concerning the interpretation of this phenomenon, yet despite that they have not reached any definitive conclusion about it!
This is indicative of man’s great ignorance of many things, and his inability to explain many of the secrets of the brain and other faculties. 
For more details, please see this category: Training Oneself
And Allah knows best.