unsleepy

The story

1. Old English · inherited fromunslǣpiġ“sleepless”
2. Middle English · inherited from*unslepy
3. English todayunsleepy

From un- + sleepy, perhaps continuing Middle English *unslepy, from Old English unslǣpiġ (“sleepless”). Compare Dutch onslaperig (“unsleepy”), German unschläfrig (“unsleepy”).