“I feel like I have been here before.”
Yes, de ja vu. The feeling that you are experiencing something you have experienced previously.
I happen to think it is a 2-way street. You may also experience something that you will again experience in the future. This can occur when your intersection actually breaks into our very same universe at a different time, but also passes through another.
Since the time-space factor of different universes is NOT in sync with our own, you could be feeling something from the past, or the future. This again comes from the intersection of universes. The intersection is typically occurring within your own personal space. I say “personal space” because it can be happening immediately around you and therefore encompassing your body as well. This accounts for the strange feeling the often accompanies your de je vu experience.
And these experiences can be quite strange indeed. Perhaps you experience something that under any normal conditions would seem impossible or irrational. I think this would be you experiencing a different universe that follows different rules. Time perception is different. Speed of light is different. People (or whatever beings are present) are much larger, or much smaller, than we know.