Did you mean Fall in Love or something? if you mean Fall in Love, then it is literally "Nahulog sa pag-ibig" but you can say "Nahulog ang loob ko" to sound more natural. :)

Literally, it would be: Bumabá ang pag-ibig. However, if you are using it idiomatically, there may be another way to say it depending on your intended meaning. We don't use accent marks in our spellings, but I placed one in "bumaba" to guide you on its correct pronunciation. Bumabá = to step down; to descend. Bumába = to recede; to reduce/decrease in value or measure.