Today's Office Fantasy

I had a mundane day at work but during my lunch break, I indulged in something unexpected. Sitting alone in my car, I fantasized about a coworker, let’s call her Sarah, in an explicit scenario that wasn’t reflective of our reality. It felt vivid and intense, leaving me wondering why such thoughts consume me sometimes. Is it normal to create these fantasies when everything else feels so routine? What should I do if this becomes more frequent?