I was an only child. Isolated. Moved a lot. I daydreamed constantly from the age of about 11 to adulthood. Elaborate long running daydreams. Full on world building with multiple characters and plot lines that carried over from day to day. And yes, dialogue was part of it.
You’re not ill, you’re coping with stress and this is a lot healthier way to do so than many. You’re turning inward because outward is difficult right now.
But to add to your coping mechanism, I recommend taking up writing as a hobby. Build yourself some worlds on paper. Creative writing can ease a lot of boredom and be a great outlet for that creative imagination and to alleviate stress. Write some stories. They don’t have to be any good. But throw some of that mental load onto paper, it’ll help. Poetry can be fun too but I found world building and writing stories the best.
It gives some structure and could potentially get people off your back. You’re plotting your stories not muttering madness. You just have lots of ideas and creativity brewing! You’ll be alright.