Green’s Dictionary of Slang

1. madness, eccentricity, orig. a form of madness that afflicted soldiers stationed in India, and spec. at Deolalie; note cit. 1925 may be incorrectly used as adj.

1911		Manchester Courier 1 Feb. 6/7: The expression ‘to be a it Dhoolallie’ ir ‘to have got the Dhoolallie tap’ is one which has spread from military slang.
1915		Lichfield Mercury 4 May 5/2: Doolally Tap — When a soldier becomes mentally unbalanced he is said to have received the ‘Doolally Tap’. The word is a corruption of the name of an Indian town, Deolali.
1923		Notts Eve. Post 27 Mar. 5/3: I have been in foreign countries [...] I have had the ‘doolally tap’.
1925		(con. WWI) Fraser & Gibbons Soldier and Sailor Words 75: Deolali Tap (otherwise Doolally Tap): (Hind.—Deolali—a sanitorium and rest-camp in Bombay; tap—fever). Mad. Off one’s head. (Old Army).
1933		(con. WWI) F. Richards Old Soldiers Never Die (1964) 195: Once in India he had a touch of the sun, which we old soldiers called the ‘Deolalie Tap.’.
1936		J. Curtis Gilt Kid 181: What’s up with you for Christ’s sake, kid? Come doolally tap?
c.1943		‘Bill O. Lading’ You Chirped a Chinful!! n.p.: Dulalley Tap: Sun stroke.
1947		Western Daily Press 7 June 5/7: I a recent police court-case [...] he pleaded that ‘he almost had doolally tap’.
1963		C. Wood ‘Prisoner and Escort’ in Cockade (1965) I iii: Doolally tap. It’s the strain see – and it gets the doolally lads first.
1971		(con. WWII) B. Aldiss Soldier Erect 80: ‘Nothing wrong with me, sergeant, it’s just the old Doolally Tap.’ Trembling and juddering [...] in imitation of someone in the extremes of deterioration.
1980		Barltrop & Wolveridge Muvver Tongue 91: Terms for mental troubles show even greater insensitivity. [...] ‘doolally tap’.

2. sunstroke.

1927

(con. WW1) P. MacDonald Patrol 101: ‘Sun’s not near high yet. ’F you start now you won’t get the tap by bein’ in the buff’ [Ibid.] 114: ‘Come on Cookie. You’ll get a Doolally in a minute. Put y’r shirt [...] on, f’r Chrisake!’.