Beside one's self

[SJudy]

Where did the phrase 'I'm beside myself, she's beside herself, etc' come from?

[Quizmonster]

This has been used since the 15th century to mean maddened/out of one's senses. A similar phrase in French: 'hors de soi' - literally 'out of oneself' - means just the same thing. The idea is that you and your mind are somehow 'adrift' from each other, as it were. The earliest-recorded version of the phrase in written English was in a Caxton publication of 1490 called 'Enydos'. In a sense, therefore, that's where it 'came from', though it may have existed before that in spoken form, of course.