It's such a pleasant, necessary escape for me. I also have lots of original worlds, but fanfic is so much lower pressure compared to origfic. It's like the difference between having to plan and cook a meal from scratch, and having someone give you fresh baked cookies. And also, as others have mentioned, most of the people I'm currently friends with are friends I made through fandom. Most of my professional opportunities have also been by way of people I met in fandom. My life would be so different without it that I can hardly imagine it.

And yeah, I'm one of those people who tells myself super-iddy fanfic stories to fall asleep at night. I've been doing it ever since I can remember.