unbelievable vs unimagined

unbelievable and unimagined both are adjectives.

Word	Noun	Adjective	Verb	Adverb
unbelievable	No	Yes	No	No
unimagined	No	Yes	No	No

unbelievable (adjective)	unimagined (adjective)
beyond belief or understanding	not imagined even in a dream
having a probability too low to inspire belief