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The Perfect Nap: Sleeping Is a Mix of Art and Science

Why Some Snoozing Sessions Leave You Groggy While Others Help

There's an art to napping.

Studies have found different benefits—and detriments—to a nap's timing, duration and even effect on different people, depending on one's age and possibly genetics.

"Naps are actually more complicated than we realize," said David Dinges, a sleep scientist at the University of Pennsylvania's Perelman School...