This reminded me of something I've been meaning to talk out for a while. Other worlds do live in my head. I've written a lot, people tell me it's good, I get the itch to write new things, and so on. There are stories in my head that I know want to come out. I do darn good description, and can write philosophical rants and essays until my fingers fall off.
The characters don't come alive. They're like puppets - I put words in their mouths, make them move, and they comply without protest. They don't talk back. They don't tell me about themselves. It feels wrong, and makes me horribly sad. And without characters, there's no story, just shadows moving on the wall of the cave. And so I don't write fiction anymore, even though I desperately *know* there are things in me that want to come out, want to be told.
I remember, dimly, that characters did come alive for me, once. Maybe a decade ago. I'm not sure exactly when, or how, that went away. There's no great turning point, no crisis or trauma, that I can point to and say "There! That's what killed my characters!" They're just gone, and I want them back.