Great sex -- oh, who am I kidding, even just good sex, or having a good time in a sexual encounter -- can really spin your head. It's not just you, I absolutely promise.
But for sure, if and when we're going to engage in more casual sex, and/or if you're struggling with moving too fast (which you already know some of the downfalls of, and those can include winding up making relationships big or serious before you even know if that's something you really want or that seems likely to work with somebody), you may need to be extra strict with yourself about getting carried away.
I think we've known each other long enough for this to be welcome instead of weird, but apologies if I'm guessing wrong about this. I've been where you're at at times, and certainly had to do some learning about how to not rush ahead or put myself *too* out there right from the start. I'm heading back into some casual things myself after having been outside of that for a while, and I have thought back about times like these lately, just to sort of remind myself that while I think I have it all down pretty well at this point, and usually do, it's always smart for me to remember that I do sometimes need to have some caution when it comes to my heart and when it comes to wanting to make things stick that a) maybe weren't meant to be sticky, or b) maybe I don't actually really know yet I want sticky in the first place. (Sticky is maybe a really lousy choice of words for all this, but oh well.)
I'd love to tell you that I had some formula for working that out you could just duplicate, but in my case, it mostly just took a good deal of feeling like an ass, winding up making some things serious fast that I was then like, "Oh crap, this is not a good thing and now I have to get out of it!" and just a lot of time and practice. And plenty of heartbreak. But now, just reminding, I think, something it sounds like you're at with yourself, as well. I think you can do this.
One thing that did help me during those times, though, was recognizing that actually, trying to nail things down way too early was more likely to assure a further relationship did NOT happen than that one did. Having been on both sides of that situation a few times, it can feel really suffocating, even a little scary, IME, from the other side. It can make you question that person's stability, or their interest in you as a person rather than you as just someone available. More times than not, I think it's fair to say that giving things way more room to breathe and grow makes it more likely that when you find the good stuff, it'll be able to grow into something good and bigger than trying too hard to make it happen. You need to have some faith, including in yourself, probably, as a desirable partner.