我を忘れる (to lose oneself)

A set idiom literally 'to forget oneself,' meaning 'to lose oneself, to be beside oneself, to lose all self-control' — typically through powerful emotion (joy, anger, grief), to the point that self-consciousness drops out. Uses the literary first-person pronoun 我 (われ). Often used with で marking the cause: 怒りで我を忘れた ('was beside oneself with anger').