Lethargic

Affected by lethargy; sluggish, drowsy, and lacking energy or enthusiasm. Characterized by inactivity and indifference.

From Greek 'lethargikos' meaning 'forgetful,' from 'lethe' (forgetfulness) and 'argos' (idle). In Greek mythology, Lethe was the river of forgetfulness in Hades. The medical sense of drowsiness and sluggishness developed from the idea of being forgetful due to sleepiness.