We may have been designed to sleep in a biphasic pattern, meaning one longer bout of sleep at night and then a short afternoon nap during the day, very much like the siesta cultures around the world. But is napping always a good thing? Well, not necessarily. Although we and other scientists have discovered that naps can have benefits for both the brain and for the body, naps can be a double-edged sword. Long naps in the afternoon or in the early evening can just take the edge off your sleepiness. It's a little bit like snacking before your main meal. So if you are struggling with sleep at night, the best advice is not to nap during the day. Instead, build up all of that healthy sleepiness so that you give yourself the best chance of falling asleep easily and then staying asleep soundly across the night. But if you're not struggling with sleep and you can nap regularly during the day, the naps of around 20 minutes taken early in the day can be just fine.