Green’s Dictionary of Slang

1. in the mind, intellectually.

1895		‘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’.
1921		P. & T. Casey Gay-cat 104: She must be a little queer upstairs.
c.1930		(ref. to late 19C) N. Kimball Amer. Madam (1981) 15: They were often wild girls, a bit batty upstairs.
1933		Bulletin (Sydney) 6 Sept. 40/3: ‘He’s strong all right [...] but he don’t seem to have a mammoth interlect.’ ‘He ain’t too sound upstairs, I’ll admit,’ Sam comes back.
1945		R.M. Lindner Stone Walls and Men 271: He was a dumbbell, a moron and wasn’t all there upstairs.
1956		J. Stearn Sisters of the Night 66: He said [...] tapping his head, ‘here’s where they got to cure you – upstairs.’.
1967		(con. 1950s) McAleer & Dickson Unit Pride (1981) 288: You’re missin’ something upstairs.
1975		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.
1989		B. Bryson Lost Continent 267: [A] cleaning lady [...] who didn’t have a whole lot upstairs but was possessed of a good Catholic heart.
1993		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.
2018		C. Hammer Scrublands [ebook] ‘Nice enough bloke, Jason, but not quite right upstairs’ .
2023		F. Bill Back to the Dirt 116: ‘Son of a bitch is a tool. Half-baked upstairs’.

2. into a senior position.

1993

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