From a compound of apo and hupnos; properly, to become awake, i.e. (by implication) to drop (off) in slumber -- fall asleep.
see GREEK apo
see GREEK hupnos
a. to awaken from sleep (Anthol. Pal. 9, 517, 5).
b. to fall asleep, to fall off to sleep: Luke 8:23; for this the ancient Greeks used καθυπνόω; see Lobeck ad Phryn., p. 224. (Hermas, vis. 1, 1 [ET].)