I happened to run into this post, but I sorta have the same thing happen to me. When it does I usually start to write the stories down and share them with my good friend. They usually tell me I should DM for them afterwards since they like D&D but that is besides the point. I find that I only do it when my mind has nothing better to focus on, like when I a bored or before bed. As long as it doesn't interrupt your day to day I think it is fine and should just be considered a distraction like daydreaming.