Crush when in a happy relationship

I'll try to make this short. I'm in a good relationship (together 5 yrs, getting married in a few weeks). But I've had a fluctuating crush on a guy I work with for around 2 years. I wasn't that worried about it, I obviously felt guilty, but I had thought long and hard about it, and even if the guy wanted to be with me and offered me everything my fiancé did and more, I would choose my fiancé. So I don't think I have any real feelings for him, it's just a silly crush. Anyhow, my wedding is getting closer and I can't stop dreaming about my crush (I don't normally think about him through the day). I feel terrible because I'm lying next to my fiancé dreaming about another guy, but I can't help it! It's only happened for 3 or 4 nights but obviously I'm worried that my subconscious is trying to tell me something. Is this normal?