To lose self-control or composure because of excitement, passion, or being absorbed in something.
試合に夢中になって、我を忘れて応援してしまった。
I got so absorbed in the game that I lost control and cheered wildly.
彼は歌うと我を忘れるほど感情が高ぶるタイプだ。
He’s the kind of person whose emotions run so high when he sings that he loses himself.
酔って我を忘れてしまい、あとで恥ずかしい思いをした。
I drank too much and lost control of myself, which was embarrassing later.