Fifty to 70 million adults in the U.S. have difficulty sleeping, and many say they're not getting the recommended seven hours a night. The biggest mistake is when people assume they can function fine on fewer hours.

"A lot of people who get that much sleep feel like it's enough for them. But when you test them, you can see night after night of getting only 5 or 6 hours of sleep, you can see declines in their performance on cognitive testing," said Dr. Puneet Patni, a sleep medicine physician in Houston.

While nothing can replace a good night's rest, Dr. Patni says a mid-afternoon nap can be beneficial, but you should keep it under 30 minutes.

"If you let it go too long, a lot of times you enter deep sleep or slow wave sleep and then you can find yourself waking up feeling even worse than before your nap. you wake up with that fogginess and really sluggish and groggy, you feel like a truck hit you,” advises Dr. Patni.

So what is the best time of day to nap? Doctor Patni says the "after lunch" struggle is real. He explains that we have two times per day that our circadian rhythm changes: at night and early afternoon. Patni said a power nap about 1 or 2 p.m. can help maintain peak performance.

"There's a natural little dip in the core body temperature around one or two o'clock. The other big decline in body temperature is at night time. You know, from 10 o'clock onward the body temperature really drops," explains Dr. Patni

While naps do not necessarily make up for inadequate or poor-quality nighttime sleep, a short nap of 20-30 minutes can restore alertness, prevent burnout, heighten sensory perception and help to prevent heart disease.