Whenever you put big physical or mental demands on your body your body temperature will rise above the norm. As a response to any intensive physical activity, the body temperature drops for a while as soon as you stop the activity.

Whenever your body temperature begins to fall, you will feel tired, lethargic, and drowsier. Your body temperature may rise and drop several times in the day as a response to the activities you're doing at the time.

Don't mistake the fall of body temperature at certain times during the day as an indication that you're not getting enough sleep.

For example, if you work an 8 hour shift at a job that requires intense activity, one might feel totally drained and ready to fall asleep when you come home at around 4 PM. What you'll actually find is that this feeling of tiredness is not a sincere desire to sleep, but rather a response from your body due to the drop of body temperature.

Giving in to the desire for sleep at this point in the day can upset your normal sleep cycle and result in reduced energy, inability to concentrate, and make you more irritable. This is the exact opposite of what you were trying to gain.

A better solution is to take a Power Nap.

To understand the difference between a Power Nap and sleep you have to know a little about sleep cycles.

Sleep comes in five stages that recur cyclically throughout a typical night. The initial stage features the sinking into sleep as electrical brain activity, eye and jaw-muscle movement, and respiration slow. The second is a light but restful sleep in which the body gets ready -- lowering temperature, relaxing muscles further -- for the entry into the deep and dreamless "slow-wave sleep," or SWS, that occurs in stages three and four. Stage five, of course, is REM, when the eyes twitch and dreaming becomes intense. The five stages repeat every 90 to 120 minutes

A Power Nap seeks to include just the first two stages of sleep.

Experts believe that the optimal Power Nap should roughly coincide with the first 20 minutes of the sleep cycle in order to give you full access to stage two's restorative benefits. In addition to generally improving alertness and stamina, stage two is marked by a certain electrical signals in the nervous system that seem to solidify the connection between neurons involved in muscle memory.

Always limit your naps to 45 minutes or less to avoid entering deep sleep.

After you wake up from your Power Nap it's normal to feel lethargic or drowsy, this is because your melatonin levels are higher. Get as much high intensity light as possible the moment you wake up, and make sure to MOVE your body to get your body temperature up and running again.

It is understandable if you feel tired even when you lead a sedentary lifestyle. This does not mean you need more sleep, but means that you need more movement and less sleep. This happens due to frequent dropping of body temperature.

The next time you feel the need for sleep during the day, try a Power Nap instead. You'll be glad you did.