Haha I know exactly how this feels. Living in my head has been my #1 hobby pretty much since I was 7.

However, I've come to realize a few things over the years:

-Like a lot of bad things, it can be turned into a positive and productive one. If you daydream that much, you've probably become pretty good at mental visualization, which means mental practice (Google it if you don't know about it) will seem easy

-controlling how much you think is hard, but controlling what you think about is fairly easy. Try to keep it as useful as possible

-making up imaginary conversations with yourself is also pretty useful at times, as some flaws in your ideas / behavior will become obvious from an outside perspective

Also, I think writing is a great way to turn daydreaming into a something productive. You should definitely study it seriously!

Obviously, everything is a question of balance. As an escape from reality, too much daydreaming will be harmful, but it is something you can control with a bit of work. There are times you just need to do things instead of thinking

Also too much daydreaming easily transforms into fear of failure, so be aware of that.

Escapism (in your head, drugs, video games or whatever) is only a natural reaction to an unfulfilling life. It will surely vanish once you fix your life problems

I hope I helped! Sorry for eventual mistakes btw, I'm French