fall away vs drop off

fall away and drop off both are verbs.

Word	Noun	Adjective	Verb	Adverb
fall away	No	No	Yes	No
drop off	No	No	Yes	No

As verbs, fall away and drop off are synonyms defined as:

Other synonyms of fall away include drop away, slip.

fall away (verb)	drop off (verb)
fall to a lower standard	change from a waking to a sleeping state
diminish in size or intensity	fall to a lower standard
	fall or diminish
	retreat
	remove (cargo, people, etc.) from and leave