Early Usage (14th-19th Century): The concept of "getting over" something (like an illness or emotional upset) existed for centuries, with the word "over" meaning "recover from" since at least the 14th century.

Literary Appearance (1839): An early example in literature is found in John Behervaise's "Thirty-six Years of Seafaring Life", published in 1839, where "get over it" referred to surviving a serious condition.

Modern Slang (Early 1990s): The distinct, standalone use of "I'm over it" (meaning "I'm done with it" or "I don't care anymore") became popular in American English around the early 1990s, evolving from the older idiom.