I know exactly what you are saying, my obsessions and fantasising are something I have done since I was little, and I'm so used to it now that it is more real for me than reality. It actually has an affect on my life because I'd rather stay at home and live in this delusion more than anything else. I've been late for appointments and missed getting to the shops before they close because I am daydreaming too much.
I have become obsessed with certain people over the years, it used to be cartoons and things when I was a kid but now it's real people. I won't say who they are or anything, but I couldn't imagine NOT fantasising. I fantasise almost every moment I'm awake. I have created this whole world in my head. It's like the insane thing that keeps me sane. In fact I've never even told anyone about it until now. How I've managed to keep it such a secret. I would never see anyone about it, it would make me feel even more nuts. That and I don't know what I'd do if I had to stop.