All of a sudden

happening, coming, made, or done quickly, without warning, or unexpectedly:
a sudden attack.
occurring without transition from the previous form, state, etc.; abrupt:
a sudden turn.
impetuous; rash.
archaic. quickly made or provided.
obsolete, .
literary. suddenly.
obsolete. an unexpected occasion or occurrence.
all of a sudden, without warning; unexpectedly; suddenly.
also, on a sudden.
adjective
occurring or performed quickly and without warning
marked by haste; abrupt
(rare) rash; precipitate
noun
(archaic) an abrupt occurrence or the occasion of such an occurrence (in the phrase on a sudden)
all of a sudden, without warning; unexpectedly
adverb
(mainly poetic) without warning; suddenly
adj.

late 13c., perhaps via anglo-french sodein, from old french subdain “immediate, sudden,” from vulgar latin -subit-n-s, variant of latin subitaneus “sudden,” from subitus “come or go up stealthily,” from sub “up to” + ire “come, go.” phrase all of a sudden first attested 1680s, earlier of a sudayn (1590s), upon the soden (1550s). sudden death, tie-breakers in sports, first recorded 1927; earlier in reference to coin tosses (1834).
entirely without warning, abruptly, as in all of a sudden the lights went out . in shakespeare’s day the common phrase was of a sudden , the word all being added in the late 1600s. also see all at once , def. 2.
see: all of a sudden