sick person vs sufferer

sick person and sufferer both are nouns.

Word	Noun	Adjective	Verb	Adverb
sick person	Yes	No	No	No
sufferer	Yes	No	No	No

As nouns, sick person and sufferer are synonyms defined as:

Other synonyms of sick person include diseased person.

sick person (noun)	sufferer (noun)
a person suffering from an illness	a person suffering from an illness
	one who suffers for the sake of principle