How do you know for sure if you have an alter? Do you record yourself?

What if someone loses track of time, people look at them like theyre crazy, like they are thinking, why are you talking to me you don't even like me.

They feel a presence of someone. Feel that person take them over, wake up not remembering.
Neighbors ask why they were out all night, saying their car was gone, but they thought they were in their bed, sleeping.

What if they hear that presence calling their name... what if you can't see them anymore, but can feel them there, watching you.

how do you know for sure?