nervousness vs mental state

nervousness and mental state both are nouns.

Word	Noun	Adjective	Verb	Adverb
nervousness	Yes	No	No	No
mental state	Yes	No	No	No

As nouns, mental state is a hypernym of nervousness; that is, mental state is a word with a broader meaning than nervousness:

nervousness: an uneasy psychological state
mental state: (psychology) a mental condition in which the qualities of a state are relatively constant even though the state itself may be dynamic

Other hypernyms of nervousness include mental condition, psychological condition, psychological state.

nervousness (noun)	mental state (noun)
a sensitive or highly strung temperament	(psychology) a mental condition in which the qualities of a state are relatively constant even though the state itself may be dynamic
the anxious feeling you have when you have the jitters
an uneasy psychological state