noun
weariness, lassitude, exhaustion, tiredness, languor, enervation, debilitation, weakness, feebleness, faintness, anoxia, combat fatigue, battle fatigue, nervous exhaustion, prostration, dullness, heaviness, listlessness, lethargy, sluggishness, ennui, burnout; see also sleepiness.
Antonyms vigor*, briskness, energy.