fall asleep vs nod off

fall asleep and nod off both are verbs.

Word	Noun	Adjective	Verb	Adverb
fall asleep	No	No	Yes	No
nod off	No	No	Yes	No

As verbs, fall asleep and nod off are synonyms defined as:

Other synonyms of fall asleep include dope off, doze off, drift off, drop off, drowse off, flake out.

fall asleep (verb)	nod off (verb)
change from a waking to a sleeping state	change from a waking to a sleeping state