hyperemesis vs regurgitation

hyperemesis and regurgitation both are nouns.

Word	Noun	Adjective	Verb	Adverb
hyperemesis	Yes	No	No	No
regurgitation	Yes	No	No	No

As nouns, regurgitation is a hypernym of hyperemesis; that is, regurgitation is a word with a broader meaning than hyperemesis:

hyperemesis: severe and excessive vomiting
regurgitation: the reflex act of ejecting the contents of the stomach through the mouth

Other hypernyms of hyperemesis include disgorgement, emesis, puking, vomit, vomiting.

hyperemesis (noun)	regurgitation (noun)
severe and excessive vomiting	the reflex act of ejecting the contents of the stomach through the mouth
	recall after rote memorization
	backflow of blood through a defective heart valve