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.
A violent tantrum; hysterics; Catfit, duck-fit: Please don't throw a conniption fit over the news
[first form 1833+, second 1848+; origin unknown; the later term catnip fit is a stab at folk etymology]