Caught in a Moment of Weakness with a Client

I've been working as a personal trainer at the local gym for about five years now. I pride myself on being professional and maintaining clear boundaries between my clients and me. That’s why it came as such a shock when I found myself caught up in something that feels like a major breach of these principles. My client, let's call her Sarah, has been training with me for about six months now. She's in her late twenties and always seems so determined to reach her fitness goals. We've never had any issues, until the past couple of weeks when I started noticing how much I was looking forward to our sessions. One day after a particularly intense workout, she told me she felt an ache in her lower back that made it difficult for her to sit comfortably later on. Naturally, I asked if there was anything else going on and whether we should take a break or adjust her routine. What followed next shocked both of us. As I stood up from speaking with her at the end of our session, she wrapped her arms around my waist in what seemed like a hug of gratitude. Before either of us could fully process it, there was this moment where my hands were on her back and hers were holding me close. We quickly pulled away, both blushing furiously, and neither of us mentioned the incident again until yesterday when Sarah brought up an idea for a new workout regimen that involved more personal assistance. There's no denying how attracted to each other we are now, but I'm terrified this might ruin our professional relationship or make it awkward. Is there something wrong with what happened? Or is it okay as long as we acknowledge and maintain the line between work and personal life from here on out?