The Perfect Nap: Sleeping Is a Mix of Art and Science,” by Sumathi Reddy. The Wall Street Journal, September 2, 2013
[You may have read all of this before. I saw the article 7 hours after it was posted on the WSJ website, and an hour later I had written this and placed it in the queue to be posted. The article evidently struck a chord with many secret nappers, and I saw it discussed on several TV news programs and news websites over the past few days.]
To get the most out of a nap—a horizontal life pause, an inner eyelid study, a snooze, a siesta, whatever you call it—to really do it right, you have to plan it, then deliberately go for it and not just leave it up to chance. Our sleep goes through a specific series of stages that recycles every one-and-a-half to two hours. You want to get the benefits of certain stages and then wake up.
The two main stages of sleep are, first, non-rapid eye movement (NREM) sleep and then rapid eye movement (REM) sleep. NREM sleep is further broken down into stage one, a light sleep, stage two, an intermediate sleep, and, finally, a slow brainwave deep sleep. Awakening from slow-wave deep sleep results in sleep inertia or sleep drunkenness—that groggy feeling that can take awhile to shake off.
REM sleep is a light sleep associated with dreaming, and this is what you want to avoid. If you dream, the nap is too long and you will feel disoriented afterward. If you are unusually sleep-deprived you may pass through the stages more quickly than suggested here.
In summary, you drop through several stages of deeper and deeper sleep, and finally come sharply back up to shallow REM sleep where you may walk, talk, and dream. Then the cycle starts all over again.
The best time to nap without interfering with nighttime sleep depends on when you go to bed and wake up, but for most of us it is in the afternoon between 1 pm and 4 pm, exactly when we want to nap, anyway.
The 10 to 20 minute nap. This is the “power nap” that gives you the most benefits in the shortest time. It is ideal for a quick burst of renewed energy and alertness. It takes you only through the lighter stages of NREM sleep so you wake up refreshed without feeling groggy.
The 30 minute nap. A nap this long can take you into the deeper slow-wave sleep, causing sleep inertia grogginess that can last up to 30 minutes, obscuring the benefits you expect from the nap.
The 60 minute nap. This takes you well into the slow-wave deep sleep that is best for restoring memory of facts, faces, and names. It would be a good nap to take before something like an exam, as long as you have a loud alarm clock and leave enough time to get over the grogginess.
The 90 minute nap. This is serious napping if you have the time. It is the best nap to restore emotional well-being, procedural memory (e.g., playing the piano), and creativity. Time it just right and you will be past the deep slow-wave sleep so you will wake up without the grogginess of sleep inertia, yet not waste time with REM dreaming and disorientation.
Young people up through their 20s prefer longer naps; as we age, we prefer shorter naps. Napping while at least a little upright, as in a lounge chair, will help prevent sliding into the deep stage of sleep. By taking a nap, you will be joining about 1/3 of Americans who say they nap daily.