Disclaimer of things doctors tell me: adhd, depression/anxiety, BPD(i sorta disagree now) suspected autism, waiting on an eval.
I can relate to some extent. I tend to daydream a lot and get really sucked into the world or the lore or even imagining a specific scene from a story. So much so that I'd zone into it and just pace around the apartment. That and just doing stimmy stuff while pacing.
I also sort of run through dialogue in my head, and sometimes that "leaks" as me verbally saying a line a character would say, or repeating it with an altered tone, or doing a couple parts of a conversation.
When I worked at a gas station I got jumpscared a few times by coworkers or customers who came in when the door beeper was broken or I was doing dishes, and they seemed fairly creeped out, but I also might've just been panicking at being seen or heard so... I dunno.
I've heard the term maladaptive daydreaming used before, but I don't think it's an officially recognized term or anything. I feel like there was a more neutral term that meant "intense daydreaming" but I forget what it was >.<