Green’s Dictionary of Slang

sousy adj.

drunk(en).

1824		J. Wight Mornings at Bow Street 217: [At] the Change house he found the ingle bleezing finely, and the whiskey o’ the best, and the gude wife unco sousie.
1955		D. Niland Shiralee 107: Kelly was still in the holts of sousy well-being.