go spare

Net Forceを読んでいます。Roddyと親しくなろうとしていたAlainの挙動がいよいよおかしくなりました。
Alain, easing him the rest of the way to the floor, once shining but now spattered with food and scattered with broken china. Alain lay there stiff-necked, jerking, trying to say things but suddenly unable to do anything but make strangled noises. "He's gone spare," Fergal said in astonishment, the Yorkshire accent coming out much more clearly than usual.
上に出てきた "gone spare" の "spare" は私の知っている意味ではありません。 たぶん "go spare" は慣用句でしょう。辞書を見ます。
・Oxford English Dictinary: Become extremely angry or distraught: 'he’d go spare if he lost the money’
・Cambridge Dictinaries: to get very upset or angry: She goes spare if I'm so much as five minutes late.
"go spare" が何故この様な意味を持つのか不思議に思えたので調べると、次の説明を見つけました。
“Go spare” doesn’t have any relatives in American slang, but the underlying logic of the phrase is sadly familiar on this side of the Atlantic.  The original sense of “go spare,”when it first appeared in British slang in the 1940s, was “to be or become unemployed,” making it a close cousin of the more formal British euphemism for being laid off, “to be made redundant.”  By the late 1950s, the normal emotional reaction to losing one’s job had colored the term “go spare,” and it had had acquired the added meaning of “to become distraught or very angry” (“When he saw what I had done he went spare,” 1958).
（http://www.word-detective.com/2009/04/do-ones-nut-go-spare/　からの引用）
なるほど、元は職を失うことを意味したのですか。