It’s no wonder siestas are such a popular tradition in many countries: A 20-minute afternoon nap does wonders to open your mind to take in new information, even after normal sleep the night before. If you limit your nap to 20 minutes, you won’t enter the deeper stages of sleep and will wake up without grogginess, says Maas. Some insomniacs actually find that a nap reduces sleep anxiety and allows them to doze off more easily at night, he says. (That’s not the case for everyone, though. Skip the nap if makes it harder to sleep at night).