nightmare vs situation

nightmare and situation both are nouns.

Word	Noun	Adjective	Verb	Adverb
nightmare	Yes	No	No	No
situation	Yes	No	No	No

As nouns, situation is a hypernym of nightmare; that is, situation is a word with a broader meaning than nightmare:

nightmare (noun)	situation (noun)
a terrifying or deeply upsetting dream	a job in an organization
a situation resembling a terrifying dream	physical position in relation to the surroundings
	the general state of things; the combination of circumstances at a given time
	a condition or position in which you find yourself
	a complex or critical or unusual difficulty