get behind vs fall behind

get behind and fall behind both are verbs.

Word	Noun	Adjective	Verb	Adverb
get behind	No	No	Yes	No
fall behind	No	No	Yes	No

As verbs, fall behind is a hypernym of get behind; that is, fall behind is a word with a broader meaning than get behind:

get behind: to lag or linger behind
fall behind: hang (back) or fall (behind) in movement, progress, development, etc.

Other hypernyms of get behind include dawdle, fall back, lag.

get behind (verb)	fall behind (verb)
to lag or linger behind	retreat
	hang (back) or fall (behind) in movement, progress, development, etc.