nightmarishness vs hellishness

nightmarishness and hellishness both are nouns.

Word	Noun	Adjective	Verb	Adverb
nightmarishness	Yes	No	No	No
hellishness	Yes	No	No	No

As nouns, nightmarishness and hellishness are synonyms defined as:

nightmarishness and hellishness: The property of being extremely bad, miserable, difficult or terrifying; resembling a nightmare.

nightmarishness (noun)	hellishness (noun)
The property of being extremely bad, miserable, difficult or terrifying; resembling a nightmare.	The property of being extremely bad, miserable, difficult or terrifying; resembling a nightmare.