conniption (n.) 1833, American English, origin uncertain; perhaps related to corruption, which was used in a sense of “anger” from 1799, or from English dialectal canapshus “ill-tempered, captious,” probably a corruption of captious. Captious means tending to find fault with little things – a good synonym is carping.
Another American corruption of British dialectical forms – one wonders why the Americans couldn’t simply learn to speak English. In any case, I love the word conniption – while not onomatopoeic, the sound of the word itself tends to convey the action it represents. My personal synonym for having a conniption is to have a Fitzcarraldo – the title of a 1982 movie by Werner Herzog about Brian Sweeney Fitzgerald, the rubber baron (yes ‘rubber’ – not ‘robber’), who tried to build an opera house in the middle of the Peruvian jungle – the locals called him Fitzcarraldo. Instead of saying ‘don’t have a fit’ (a mostly useless admonishment to excitable types) I say ‘don’t have a Fitzcarraldo.’ I like to think this makes me quirky, although it probably simply renders me incomprehensible to most people.