Researchers said their findings support previous studies, which have found that sleep deprivation makes it harder for people to control negative emotional responses. The National Sleep Foundation in Arlington, Virginia, makes the same recommendations:

           "As a nation, the United States appears to be becoming more and more sleep-deprived. And it may be our busy lifestyle that keeps us from napping. While naps do not necessarily make up for inadequate or poor-quality nighttime sleep, a short nap of 20 to 30 minutes can help to improve mood, alertness and performance."

It offers these tips for effective workplace napping:

• A short nap (20 to 30 minutes) usually is recommended for short-term alertness. This type of nap improves alertness and performance without leaving nappers feeling groggy or interfering with nighttime sleep.

• Provide a restful place to lie down, with a comfortable temperature. Try to limit the amount of noise heard and the amount of light filtering in. While some studies have shown that just spending time in bed can be beneficial, it is better to try to catch some zzz's.

• Late-day naps might affect nighttime sleep patterns and make it difficult to fall asleep at bedtime. If it's too early in the day, the body may not be ready for more sleep.

The benefits? Sleepy military pilots and astronauts found that a 40-minute nap improved performance by 34 percent and alertness by 100 percent in a NASA study.