"lose sleep over" is a phrase used to express worry or concern about something. It can be replaced with numerous synonyms that convey similar meanings. One such synonym is "agonize over," which denotes deep mental distress or anxiety caused by a particular situation. Another alternative could be "fret about," which conveys a sense of anxiety or worry relating to a specific issue. "Lament over" can also be used as a synonym for "lose sleep over," indicating a feeling of sadness or regret about something. Other synonyms include "dwell on," "obsess about," and "brood over," which all convey a sense of deep contemplation or concern.