beside oneself, to be

To  be  distraught  with  worry, grief, anger, happi- ness,  or  some  other  strong  emotion. The  expression  appears  in  the  King James version of the Bible (Acts 26:24): “Paul, thou art beside thyself; much learning makes thee mad.” It uses the adverb beside in an older sense, mean- ing “outside of,” so literally the phrase means “outside of oneself,” the self in question being one’s mental faculties.