drop down vs sag down

drop down and sag down both are verbs.

Word	Noun	Adjective	Verb	Adverb
drop down	No	No	Yes	No
sag down	No	No	Yes	No

As verbs, sag down is a hyponym of drop down; that is, sag down is a word with a more specific, narrower meaning than drop down:

Other hyponyms of drop down include drop open, fall open, droop, flag, sag, swag, sag.

drop down (verb)	sag down (verb)
fall or descend to a lower place or level	cause to sag