Hi. There's the type who replace the original occupant, and there's the type (such as myself) who show up from somewhere else and move in to co-exist just fine with the original occupant.
You're basically describing trauma-based DID, not an actual walk-in.
Many people are aware of things like parallel universes and a collective consciousness without the use of drugs or psychosis.
Since you're very new to the subject, maybe talk to some of us before trying to analyze something you don't have much knowledge of.