Matt has hit the nail on the head. "Get Up John" is an instrumental tune that Monroe based on "Sleepy John," a tune his Uncle Pen played. The words came after the fact. Not nearly as good as the tune.

He tuned his mandolin to an open D tuning for it. The high E strings are tuned down, one to D, the other to A in unison with the A strings, which, like the D strings, are not altered in pitch. One of the G strings is tuned up to an A, the other down to an F#.