Taking the right kind of nap depends on your goals. For the office, the 10-20 nap seems most reasonable. On a weekend afternoon, an hour-long nap, or even an REM nap of 90 minutes or more, may be more appropriate. To wake up perky from naps, experts recommend two tricks: One is to drink caffeine before your nap. Caffeine won't interfere with short naps and will lessen the effects of sleep inertia. The other trick is to sleep partially upright. Studies conducted by sleep researchers have shown that not lying totally flat results in avoiding falling into a deeper sleep.