IDIOMS

forget oneself

(idiomatic) to lose one's dignity, temper, or self-control.

Example: 2011 August 28, Vincent Hogan, “'Where Rovers go from here could be thrilling or terrifying'”[1], Irish Independent:
  You see, the easy thing would be for Rovers to forget themselves.
2005, Elbow, Forget Myself
  No I know I wont forget you but I'll forget myself if the city will forgive me.
To become unmindful of one's own personality; to be lost in thought.