Ian

@psmears and Rodney. Good points both, and thanks for the feedback.

@WS2 Yes, but that might not necessarily exclude the power-breaker analogy, since 'down with the flu' or 'up and about' both seem to speak more of a horizontal or vertical position of the body.

Might it be an allusion to the position of a power breaker? Up is on, down is off.

I use the following joke to help remember that tricky word: "A knight in shining armor has never had his mettle tested"