Here's everything science knows about napping -- where to do it, how to do it, how long to do it and if you should risk goofing up your internal clock.
A short afternoon catnap of 20 minutes yields mostly Stage 2 sleep, which enhances alertness and concentration, elevates mood, and sharpens motor skills. To boost alertness on waking, you can drink a cup of coffee before you nap. Caffeine requires 20 or 30 minutes to take effect, so it will kick in just as you're waking. Naps of up to 45 minutes may also include rapid eye movement (REM) sleep, which enhances creative thinking and boosts sensory processing.
Limit your nap to 45 minutes or less, if you need to spring into action after dozing. Otherwise, you may drift into slow-wave sleep. Waking from this stage results in sleep inertia, that grogginess and disorientation that can last for half an hour or more.
From the Upcoming Queue, submitted by knitmeapony.