If you’re a napper, you’re in the company of some high achievers. Albert Einstein, Napoleon Bonaparte, Thomas Edison and Winston Churchill all took daily naps.

Research shows that no matter how long you sleep at night, your body’s programmed to get sleepy in the early afternoon. A short nap – sometimes called a power nap – can give you alertness and energy. Studies suggest that a 30-minute nap is usually more restorative than a nap of, say, of two to three hours.

That’s partly because with a long nap, your sleep can progress into deeper slow-wave sleep, which contributes to “sleep inertia”, that grogginess you feel for a while after waking up. Even a short nap can produce some sleep inertia, but it doesn’t last long. You can overcome it by increasing metabolic activity in your body and brain. That is, get up, move around and splash water on your face.

If you’re trying to battle your afternoon sag in energy by jump-starting your system with coffee, you’re actually being counterproductive. According to sleep experts, you’re just creating an illusion of efficiency and alertness, and depriving your body and brain of much-needed sleep.

Experiments with airline pilots also show that short naps – nicknamed “power naps” – can help people boost their brain function. That’s especially true for healthy people who aren’t getting enough sleep. But even though naps can be great energizers, they’re no substitute for longer periods of healthy sleep.