wakefulness vs arousal

wakefulness and arousal both are nouns.

Word	Noun	Adjective	Verb	Adverb
wakefulness	Yes	No	No	No
arousal	Yes	No	No	No

As nouns, arousal is a hyponym of wakefulness; that is, arousal is a word with a more specific, narrower meaning than wakefulness:

wakefulness: a periodic state during which you are conscious and aware of the world
arousal: awakening from sleep

Other hyponyms of wakefulness include vigil.

wakefulness (noun)	arousal (noun)
a periodic state during which you are conscious and aware of the world	the act of arousing
the process of paying close and continuous attention	mutual sexual fondling prior to sexual intercourse
a temporary state in which you are unable (or unwilling) to sleep	awakening from sleep
	a state of heightened physiological activity