The most powerful thing that has stopped my daydreams is having them crushed.
So what did I do?
I replaced them with other daydreams, actual, realistic ones that can actually come true, like having a girlfriend or joining the military after graduation. I realized that dreaming of reality gives you better footing than dreaming of your fantasies in the clouds that can't actually happen. They were meaningless and a waste of time. So now I enjoy life instead of letting it all pass me by and have set actual goals for myself, it has brought me back to earth again.