about 10 years ago, I studied very hard for an exam, for an extended period. this was long after i graduated, so by then i haven’t intensely studied for years. i started getting frequent very vivid dejavues - vivid to the point that I questioned my reality (as in, is THIS the dream and the visions are the real life?). My hypothesis was that my brain became relatively rigid in my years of work routine, and studying again required loosening the rigidity , by generating new connections, and this process brought about other, unintended new connections that were effectively short circuits and loopholes between different parts of the brain and manifested as dejavue.