nausea vs sickness

nausea and sickness both are nouns.

Word	Noun	Adjective	Verb	Adverb
nausea	Yes	No	No	No
sickness	Yes	No	No	No

As nouns, nausea and sickness are synonyms defined as:

nausea (noun)	sickness (noun)
disgust so strong it makes you feel sick	impairment of normal physiological function affecting part or all of an organism
the state that precedes vomiting	the state that precedes vomiting
	defectiveness or unsoundness