“Do you get deja vu? 🎶”

Some people said they have but I'll ask again anyway.
So when you're on the middle of doing something, the specific actions, make you feel like you have done it before. You probably haven't, you probably have dreamt it before, sometimes you know for sure that you haven't done that before, but the feeling in your stomach keeps feeling like you've already encounter it somewhere, your mind or reality.
I'm wondering where these thoughts and feeling comes from?