also freakout "bad psychedelic drug trip or something comparable to one," 1966 (despite an amusing coincidental appearance of the phrase dug up by the OED in "Fanny Hill" from 1749), from verbal phrase freak out, attested from 1965 in the drug sense (from 1902 in a sense "change, distort, come out of alignment"); see freak (n.). Freak (n.) "drug user" is attested from 1945.
She had had her freak out, and had pretty plentifully drowned her curiosity in a glut of pleasure .... [Cleland, "Memoirs of a Woman of Pleasure," 1749]
1560s, "sudden turn of mind," of unknown origin, perhaps related to Old English frician "to dance" (not recorded in Middle English, but the word may have survived in dialect) [OED, Barnhart], or perhaps from Middle English frek "bold, quickly," from Old English frec "greedy, gluttonous" (cf. German frech "bold, impudent").
Sense of "capricious notion" (1560s) and "unusual thing, fancy" (1784) preceded that of "strange or abnormal individual" (first in freak of nature, 1847; cf. Latin lusus naturæ, used in English from 1660s). The sense in health freak, ecology freak, etc. is attested from 1908 (originally Kodak freak, a camera buff). Freak show attested from 1887.
"change, distort," 1911, from freak (n.). Earlier, "to streak or fleck randomly" (1630s). Related: Freaked; freaking.