What Does It Mean When A Coworker Is Too Into You?

So last week, one of my coworkers named Alex kept hitting on me and it got a bit too real fast. We're both in our 20s but I don't really date much anymore. Anyway, long story short we ended up hooking up at the office after hours and yeah... It was good. Really good. But then there's all this weird talk about us starting something now or just seeing each other again soon. It feels like a slippery slope to me but Alex seems genuinely excited about it all. I'm not sure how to feel, part of me enjoys the attention, another part is scared. So confusing... Maybe I should just stick with my own life? Or am I being an asshole by shutting this down too fast?