hebetude - mental lethargy or dullness

torpidity, torpor - a state of motor and mental inactivity with a partial suspension of sensibility; "he fell into a deep torpor"

weakness - the property of lacking physical or mental strength; liability to failure under pressure or stress or strain; "his weakness increased as he became older"; "the weakness of the span was overlooked until it collapsed"

inertia, inactivity, inactiveness - a disposition to remain inactive or inert; "he had to overcome his inertia and get back to work"