The way to attain a high level of faith as our righteous forebears the (Salaf) did is, firstly, by persevering in seeking to understand what Prophet Muhammad brought, then by persevering in doing what he enjoined and in refraining from what he forbade. All of that is to be done with true sincerity, having no interest in worldly gain, and hoping for the Hereafter.

If you are losing faith in Islam, you need to increase your hope and trust in Allah. You should increase your good deeds, such as reading the Quran, giving charity, remembering Allah (Dhikr), upholding the ties of kinship, etc.

There is no Islamic explanation for Déjà vu, 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.