fall back vs fall behind

fall back and fall behind both are verbs.

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

As verbs, fall back and fall behind are synonyms defined as:

Other synonyms of fall back include drop off, recede.

As verbs, fall back and fall behind are synonyms defined as:

fall back and fall behind: hang (back) or fall (behind) in movement, progress, development, etc.

Other synonyms of fall back include dawdle, lag.

fall back (verb)	fall behind (verb)
go back to bad behavior	retreat
retreat	hang (back) or fall (behind) in movement, progress, development, etc.
hang (back) or fall (behind) in movement, progress, development, etc.
fall backwards and down
move back and away from
have recourse to