What did cavemen sleep on? Cavemen slept on the floor of their caves. Sometimes, they would construct a pile of straw and leaves in the pit of a cave to make a recessed and cozy sleeping surface.

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Most people prefer to sleep on their side. This is supported by a study showing that children sleep on the side, back, and front equally, with a growing preference for the side position when approaching adulthood.

During REM sleep the brain is highly active. This stage is called active sleep. Most vivid dreams occur in REM sleep. In REM sleep, brain activity is comparable to that in waking, but the muscles are virtually immobilized, which prevents people from acting out their dreams.

Leonardo da Vinci’s sleep schedule included 20-minute naps every four hours. Da Vinci followed an extreme form of a polyphasic sleep schedule called the Uberman sleep cycle, which consists of 20-minute naps every four hours.

Sleeping for a couple of hours or fewer isn’t ideal, but it can still provide your body with one sleep cycle. Ideally, it’s a good idea to aim for at least 90 minutes of sleep so that your body has time to go through a full cycle.

In a recent study, researchers say napping two or three times a week might be good for your heart health. Experts say daily napping may be a sign of inadequate nighttime sleep or an underlying health problem. One expert says naps should be shorter than 30 minutes or longer than 90 minutes.

If you’re trying to lose weight, having a nap in the afternoon could help to boost your weight loss. A new study has revealed that people burn more calories while at rest in the afternoon than they do in the morning.

Napping, in general, isn’t considered unhealthy. Taking brief naps under half an hour can bring about many benefits, such as reduced fatigue, increased alertness, improved mood and improved cognitive performance. However, the duration of your nap can determine whether you see positive or negative effects.

Blood flow to the small intestine “dramatically increases” after a person eats, says Dr. Tomonori Kishino, a professor of health science at Japan’s Kyorin University. And as blood is pumped into the gut to fuel digestion, a corresponding drop in blood flow to the brain could trigger feelings of sleepiness, he says.

The following strategies can help prevent tiredness after a meal:

• Eat little and often. Rather than eating big meals, eat smaller meals and snacks every few hours to keep up energy levels.
• Get good-quality sleep.
• Go for a walk.
• Take a short nap during the day.
• Try bright-light therapy.
• Avoid drinking alcohol with meals.

Going to sleep directly after you eat means your body doesn’t get a chance to burn off those calories. And, eating a big meal and then hitting the couch can be just as harmful. Eating an early dinner allows your body time to burn off those unwanted calories before going to sleep.

The downtime before running depends on how much you’ve eaten and your digestive system, according to Livestron, which offers this general rule: at least an hour after a small snack, two to three hours after a small meal and three to four hours after a large meal.