nervousness vs mental condition

nervousness and mental condition both are nouns.

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

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

nervousness: an uneasy psychological state
mental condition: (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 state, psychological condition, psychological state.

nervousness (noun)	mental condition (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