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

I sometimes make up stories in my head, especially when I'm bored. I might even laugh at them when they're funny, though that only happens in private.
At first I wrote them down as practice for creative writing but now I hardly have the time to.
They are often inspired by things I see online or books/movies/shows that I like; for example, I imagine what a character's life will be like five years after the end of the movie they were in, or what I would do if I lived in their universe; kind of like fan fiction.
There is nothing in these stories that would get them a rating past R if they were written down, and they are usually comedic and contain no violence, even if about books/movies/shows that did have it.