all of a sudden vs on the spur of the moment

all of a sudden and on the spur of the moment both are adverbs.

Word	Noun	Adjective	Verb	Adverb
all of a sudden	No	No	No	Yes
on the spur of the moment	No	No	No	Yes

As adverbs, all of a sudden and on the spur of the moment are synonyms defined as:

all of a sudden and on the spur of the moment: quickly and without warning
all of a sudden and on the spur of the moment: happening unexpectedly
all of a sudden and on the spur of the moment: on impulse; without premeditation

Other synonyms of all of a sudden include abruptly, dead, of a sudden, short, suddenly.

all of a sudden (adverb)	on the spur of the moment (adverb)
suddenly	quickly and without warning; happening unexpectedly; on impulse; without premeditation
quickly and without warning; happening unexpectedly; on impulse; without premeditation