where do u stand?

[jacey]

How can you be beside yourself? As in " I was beside myself with worry?

[Chillum]

I'd imagine it to mean to step outside your normal bounds of thought. To be so concerned that all other, normal considerations become irrelevant.

[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. It's not a lot different - in the 'position sense - from being 'in two minds' about something.