Green’s Dictionary of Slang

lose it v.

1. to lose control temporarily; in an extreme case to have an actual mental breakdown, to go mad.

[[UK]Story of a Lancashire Thief 9: He had been a jigger-dubber [...] but got sacked for boozing, and then he lost himself. [Ibid.] 15: (lost himself) Went lower and lower].
[[US](con. 1920s) J.T. Farrell Young Manhood in Studs Lonigan (1936) 208: Hey, grandpa! Button up. You’re losing something].
[[UK]H. Brown Walk in Sun 102: They had their morale back. Not that they had ever really lost it. They had simply been a little uncertain of themselves].
[US]E. De Roo Go, Man, Go! 23: He signalled to Gil not to say anymore. Gil lost it.
[US]H.S. Thompson Hell’s Angels (1967) 98: The minute you hit the brakes you’ll start losing it; bikes don’t drift like cars.
[US]Eble Campus Sl. Apr. 3: lose it – unable to cope, astounded, rattled.
[US](con. 1969–70) D. Bodey F.N.G. (1988) 37: The last guy who rotated out [...] was out here in the Bush for three hundred and fifty days. [...] he was fuckin’ losing it the last couple weeks.
[UK]K. Lette Llama Parlour 80: Look, if ya think you’re gonna lose it and say somethin’ totally stoo-pid, well, I dunno.
[Ire]P. Howard Curious Incident of the Dog in the Nightdress 27: I end up totally losing it [...] and we’re talking totally.
[SA]IOL News 5 Dec. [Internet] I am a very prim and proper person [...] my clients se me as the business type. It should be interesting how it is going to look when they see me lose it.
[UK]Guardian G2 3 July 5/1: Did I lose it, am I crazy, man?

2. to lose one’s virginity.

[UK]Sun. Times Mag. 30 Sept. 34: ‘How old were you when you lost it?’ ‘Fifteen years eleven months and two weeks.’.

3. (US campus) to be surprised, to be shocked.

[US] P. Munro Sl. U.

4. (US campus) to vomit.

[US]Eble Campus Sl. Oct.
[UK]M. Belmonte Compter Science and Why (1993) [Internet] I was struck with [...] the plethora of words and phrases meaning ‘vomit’ and/or ‘to vomit’ [...] At most American colleges and universities, a weekend cannot pass without seeing multitudes [...] lose it.

5. to lose one’s skills, abilities.

[UK]J. Mowry Way Past Cool 131: You losin it, man . . . lettin some little sucker slice you like that.

6. to pass out.

[UK]K. Richards Life 489: I remember a show in Italy where I really knew I was losing it [...] The air was totally dead and I started to feel myself going.