Not to say that I understand it completely, but this is what I've found on a more scientific note.
"A different but related theory states that déjà vu is a fleeting malfunctioning between the long- and short-term circuits in the brain. Researchers postulate that the information we take in from our surroundings may "leak out" and incorrectly shortcut its way from short- to long-term memory, bypassing typical storage transfer mechanisms. When a new moment is experienced—which is currently in our short-term memory—it feels as though we're drawing upon some memory from our distant past.
A similar hypothesis suggests that déjà vu is an error in timing; while we perceive a moment, sensory information may simultaneously be re-routing its way to long-term storage, causing a delay and, perhaps, the unsettling feeling that we've experienced the moment before."
Source - https://www.psychologytoday.com/blog...science-d-j-vu
And it kinda makes sense. If somehow, what you just saw accidentally made its way to your long-term memory instead of your short-term one, then it's very likely that what you saw would actually feel like something from your distant past or probably another life.
However, that's not to say that all deja vus are complete delusions caused by misfiring of neurons. In exceptional cases, one may come across a certain place, soul or situation that rings an all-too-familiar bell, triggering memories or feelings that have been carried on from past lives. But how do you differentiate between these true deja vus and neuronal mismatches?
Well, in ancient Vedic philosophy, in order to progress down the spiritual path, one needs to develop 'viveka' or discrimination between true and false, good and bad. True spirituality is a lot like science. A real spiritual aspirant will always look for the truth, regardless of whether he or she likes it or not.
For instance, let's talk about visions.
Visions are of two types:
1) Internal: These visions are only projections of your subconscious mind. So many feelings are hidden in your mind from your past several births. These feelings are expressed as visions and appear as real external scenes. In extreme cases, this can also accelerate into a mental illness where the patient talks with another imaginary person appearing before him.
2) External: A scene appears without any relationship with your mind. This is not the projection of your mind and is not a mental illness. The scene is arranged externally and the forms appearing are energetic in nature. Such a vision is independently generated, and not based on any feeling of your mind. This appears due to some external reasons so as to give you some external information.
The real problem is that the internal vision is often mistaken as an external vision. Your own aspiration is conveyed to you in such cases. You’re simply mislead by such a false external vision.
Most people even tell lies that they had external visions in order to get some recognition from the surrounding public. They feel that it’s prestigious to have such visions, which get them some kind of special status. This should be nipped at the bud. The reason is that the spiritual path is always based on the truth only. By telling lies for such false fame, you also procure sin unnecessarily.
Even if you really have visions, you should analyze the vision to gauge whether it’s internal or external. If the result of such a vision is proved practically, you can conclude such a vision as an external one since internal visions have no practical outcome.
Unless a practical result comes out of it, it may not be a real external vision. It may just be your internal vision expressing your long-time, deeply hidden aspiration.
The practical reality of the outcome of the vision should be proved so that we can infer the reality of the external vision. The proof here should be considered in a reverse way, i.e. from the fruit (practical outcome) to cause (vision).
If the vision says that something will happen, you should wait till that happens practically in reality. Then only can you say that the vision is practically real. You should wait till the practical result is clearly seen and then only should you declare that your vision is correct. Otherwise, millions of visions are expressed by millions of people.