Narcoleptic

Modern medical compound from Greek narkê (numbness, stupor, the same root as narcotic and narcosis) and the suffix -leptikos (liable to being seized, disposed to receive), from lambanein (to take hold of, to seize). The narco- part signals the stupor; the -leptic part signals the sudden onset. Together they name a condition in which deep sleep overtakes a person involuntarily. The compound entered European medical vocabulary in the late nineteenth century, as systematic neurology named newly classified conditions.

Primarily a medical and clinical adjective. In informal speech it is sometimes stretched loosely to mean extremely drowsy or prone to falling asleep, departing from its precise clinical sense.