Hiya, Juniper. I've been thinking about your question. I don't know if it can be generalized.
I can only say that for me, I "just knew" when I've loved someone. The fluttering heart, lots of laughs, and all that stuff was the early part...a sort of infatuation, almost. After that, it was knowing that I cared about the person and wanted to be with him through good and bad.
I think it's different for each person because we're all different, and every relationship is different. Also, I think "love" changes and grows over time, so it's not the same at every stage of the relationship.