sluggishness vs inactiveness

sluggishness and inactiveness both are nouns.

Word	Noun	Adjective	Verb	Adverb
sluggishness	Yes	No	No	No
inactiveness	Yes	No	No	No

As nouns, inactiveness is a hypernym of sluggishness; that is, inactiveness is a word with a broader meaning than sluggishness:

Other hypernyms of sluggishness include inactivity, inertia.

sluggishness (noun)	inactiveness (noun)
inactivity; showing an unusual lack of energy	a disposition to remain inactive or inert
the pace of things that move relatively slowly	the state of being inactive
a state of comatose torpor (as found in sleeping sickness)