Interesting... in the dictionary I have (Webster's), "falling in love" is used as an example of the definition "to pass suddenly and passively into a state of body or mind or a new state or condition", but next to "falling in love" is another example: "falling asleep". It never occurred to me to equate the two!

Also, the expression "fall for" is defined as "falling in love" but also as "to become a victim of" (as in "he fell for the trick").

I wish the dictionary said more about the origins of the various meanings of the word "fall", instead of one origin of the word itself (Middle English fallen from Old English feallan akin to Old High German fallan and perhaps to Lithuanian pulti [how did pulti get into this?]). Without some info, I don't know if it's proper to equate the "fall" of "falling in love" with being born (like lambs "fall"), or with issuing forth (like words that fall from the lips), or with entering unawares (like falling into error), or with suffering ruin (as in "the city fell"), or with complying (like falling into line). All of the above menings sound to me like some of the aspects of falling in love!