off one's guard vs napping

off one's guard and napping both are adjectives.

Word	Noun	Adjective	Verb	Adverb
off one's guard	No	Yes	No	No
napping	No	Yes	No	No

As adjectives, off one's guard and napping are synonyms defined as:

Other synonyms of off one's guard include off-guard, off guard, off her guard, off his guard, off your guard.

off one's guard (adjective)	napping (adjective)
not prepared or vigilant	not prepared or vigilant