Is it normal that i make up stories in my head?

All the time I make up stories in my head. It can be about anything. Most of them are about me and my boyfriend doing cute couple things that I wish I could do with him in real life, but im in Cali and hes in Alaska. I start to think that im going crazy but I wanted to make sure. And because of these stories, im failing 3 classes with D-'s. How to I stop?! My mind just keeps going and its hard to just not think at all. I really need to stop making these stories but I dont know how. Ill do this in class or when Im bored with nothing to do. Ill tell everyone im sleeping but ill stare at a blank wall for two hours and think. Think, think, think, and think. Do other people do this? Am I crazy? How do I stop this? And Is It Normal???