There are two ways to nap: a quick 20 min nap doesn't take you into deep sleep (characterized by delta wave patterns--google SWS) and let's you wake with much l

There are two ways to nap: a quick 20 min nap doesn't take you into deep sleep (characterized by delta wave patterns--google SWS) and let's you wake with much less sleep inertia. It's refreshes, but doesn't consolidate memory. A longer nap (60-90 min) typically takes you into deep sleep, and is harder to wake from. However, a long nap will give you memory consolidation and recovery on par with a full nights sleep.