Green’s Dictionary of Slang

upstairs adv.

1. in the mind, intellectually.

[Aus]‘G.G.’ Sporting Sketches in Sportsman (Melbourne) (18/10/1898) 5/8: ‘He sort o’ went a bit barmy upstairs and thort he’d try what the straight lay was like’.
[US]P. & T. Casey Gay-cat 104: She must be a little queer upstairs.
[US] (ref. to late 19C) N. Kimball Amer. Madam (1981) 15: They were often wild girls, a bit batty upstairs.
[US]R.M. Lindner Stone Walls and Men 271: He was a dumbbell, a moron and wasn’t all there upstairs.
[US]J. Stearn Sisters of the Night 66: He said [...] tapping his head, ‘here’s where they got to cure you – upstairs.’.
[US](con. 1950s) McAleer & Dickson Unit Pride (1981) 288: You’re missin’ something upstairs.
[UK]G. Kente Too Late in Kavanagh S. Afr. People’s Plays (1981) 93: Of course, you are sick upstairs. It’s not the head but what’s in it.
[US]R. Klein Jailhouse Jargon and Street Sl. [unpub. ms.].
[US]S. King Dolores Claiborne 23: She probably wa’ant completely vacant upstairs, not even in the end. A few rooms to rent, maybe, but not completely vacant.

2. into a senior position.

[US]A. Rodriguez Spidertown (1994) 118: You know Spider shot him upstairs, got ’im some big contracts.