Wow I'm speechless I can't believe it, this is a real thing.
Your descriptions are spot on for at least 80%.
I don't have "pacing back and forth", I'd just sitting there or laying down, staring blankly into my monitor, or making faces and muttering the words (soundless) that my character is saying, and I'd "snap" out of it when occasionally I got "too loud", embarrassed with myself, and then continue with the story.
Not quite sure what triggers it but I can listen to music, yt videos, or twitch stream, and my mind would wander off to this character again while video or the streamer's voice keep playing in the background, unrelated at all.
Its extremely cringy and embarrassing to type this but..
Currently I'm imagining this cute asian girl with short hair, who's somehow a successful pro gamer and streamer. Started her story about 3yrs ago, somehow modeled her after a cartoon/comic artist on yt that I found years ago. This character is blending in with real life happenings and internet people that I'm a fan of and watch regularly.
I imagine she'd befriend A, B, C person because they're part of this and that group, or have similar opinions on some things (REAL world events), like if I see a tweet by them my mind starts to wander off thinking "she'd reply with something like this because her personality is X and she'd disagree with this". And then She'd dislike F, G person because they have conflicting personalities/humor.
But I understand 100% she's NOT me, this is just fantasy and I'm not trying to be her or anything like that.
And I'm kind of her cameraman/scriptwriter and viewer at the same time.
Its embarrassing/cringed me out so much to even admit this, but it gives me nice feelings in my head to imagine that if somehow this person exist in real world. And rooting for her to overcome adversaries (that I myself "wrote" for her) gives me satisfaction.
Its quite scary to think I might have to leave behind this story and stop daydreaming completely if I want to be normal again. Even now I wonder if there's a way that I can function like a normal, real person again without "giving her up".
Sorry for messy english, please help T__T