I could swear I've answered this question before. 🤔

Some reckon it's your soul recognizing a place from your previous life.

past life connections causing a phsychic vibration on genetic lineage

I believe it occurs as an event happens twice. As an example, maybe you pass a butchers driving and you think of the time your child was ill. Two years later you drive pass same butchers thinking what medicine to get for yer child who's ill again. Having completely forgotten two years ago, the mind falls into a de ja vu.

People can argue "Wait, wouldn't the event 2 years ago be remembered?" BROTHER! Let me ask, do you remember your EXACT thoughts two weeks ago at 2pm?? THOUGHT SO! THIS IS TWO YEARS AGO!

What about visiting brand new places n getting de ja vu? The senses around you "mainly smell" could trigger it. Maybe yer thinking about a person whilst smell of vanilla's in the air. Four years later you're abroad, smell of vanilla's in the air n yer thinking about that person yet again. HEY HO! DE JA VU!

It can be increased by medication (and epilepsy) so I think it's neurological.

My cat's name

Lack of sleep

Brain lag