Honestly, for me, I haven't met that beautiful someone who makes my stomach turn upside down, I guess I'm just busy or the universe believes I'm unavailable for love right now.
I get butterflies at an early stage of the relationship, but as things get settled I develop another level of feelings quite different from the initial stage. This feeling can be common especially when you met someone so perfect.
I have felt like that, maybe my time is coming, I remember those days in highschool I had a crash and that is how I would feel but you know crashes come and go so it's not something serious.