Green’s Dictionary of Slang

(US) a state of depression or disgust; thus black-assed adj., depressed, disgusted.

1945		E. Hemingway letter 2 Apr. in Baker Sel. Letters (1981) 579: Certainly have the Black Ass today, Miss Mary so much it makes me sick [...] So am being black-assed and temperamental.
1955		J. Blake letter 13 Sept. in Joint (1972) 75: I had a long spell of blackass, but it’s lighter now.
1965		D. Pearce Cool Hand Luke (1967) 15: Dragline was in a very deep mood, suffering from a bad case of the Black Ass.
1987		E. Hemingway [title] Black Ass at the Crossroads.
2002		A. Hindman weblog 10 May 🌐 Am for some reason dropping pronouns from text like Hemingway did. Saves time and reminds me that Hemingway called depression the black ass. When he was crippled in two successive plane crashes in a matter of days, he said he had a touch of the black ass.