A sudden breakdown or collapse, either physical (like a car crash) or mental (like a nervous breakdown).
From 'crack' (to break or fail) + 'up' (prefix indicating completion or intensity). Emerged in early 20th-century American English as a noun form of the phrasal verb 'crack up,' meaning to suffer a breakdown or crash.
F. Scott Fitzgerald actually used 'crack-up' as the title for a famous 1936 essay about his own mental collapse, which helped cement this American term in literary history and made it sound less medical and more poignantly human.
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