It almost sounds as if this is an aspect of Obsessive Compulsive Disorder, where you feel the strong and irresistible compulsion to do something or behave in some fashion repeatedly. Or perhaps you've been born with Aspergers, which simply means your brain is simply "wired" a bit differently than an neurotypical (average) brain, therefor, you think and do things on a different wavelength, so to speak, than neurotypical people. As a result, the world around you is strange and alien, like you're on another planet, and the world you've created is the seemingly normal one that you feel you belong to. Aspies, those with Apsergers, often tend to find one particular aspect of their life, an object, sport, or activity that they really like, and become hyper-obsessed with it. Maybe this construction of an alternate world is your obsession. Something you've done so often, you do it constantly, only emerging from it to connect with people in reality when necessary.

Then again, I'm no clinically trained psychologist, so I can't make any semblance of a former diagnosis. Maybe talking about and exploring this alternate reality you've all but consumed yourself in creating will help you figure out why you created it in the first place. Like I said before, maybe it's the world that you feel you belong to, rather than the strange and alien-like reality that is all around you.

If all else fails, you can write down everything you've created into some sort of novel, or series of novels, and make some money off of it. I believe Tolkien was similar in this aspect because he created a highly detailed alternate universe of completely unique characters, religions, languages, locations and cultures that all come together on the geographical plane known as Middle Earth. It worked out for him in the end, so it might work out for you.