A Moment of Weakness in Class

I never thought I would admit this, but last week while teaching a late afternoon class, I found myself sneaking glances at one of my students. She's bright and always participates actively, which usually keeps me focused on the material. But that day, something about her caught my attention differently than usual. Before I knew it, I was imagining scenarios beyond what’s appropriate for us both. It felt wrong, but also strangely compelling. This isn't like me at all, I'm very clear-headed and professional most of the time. What happened to my boundaries? Why did I lose focus so suddenly?