How do you have a hallucination? Not like, shrooms hallucination, like, a person from ur past comes to talk?

I don't think it's possible to literally see someone from your past, but someone you've made up in your mind I know that's possible. When I was little I loved horses and I can remember literally seeing a horse that lived in my closet and ate spaghetti. I'd talk to him and he'd talk back to me. If you spend at least an entire day isolated in a room by yourself with no distractions trying to conjure up someone to talk to.