Exercise gives your cells more energy to burn and circulates oxygen. Exercising causes your body to release stress hormones that in modest amounts can make you feel energized.

Smoking siphons off your energy by causing insomnia.

The nicotine in tobacco is a stimulant, so it speeds the heart rate, raises blood pressure, and stimulates brain-wave activity associated with wakefulness, making it harder to fall asleep.

• Avoid napping during the day.
• The first night, go to bed later than normal and get just four hours of sleep.
• If you feel that you slept well during that four-hour period, add another 15–30 minutes of sleep the next night.
• As long as you're sleeping soundly the entire time you're in bed, slowly keep adding sleep on successive nights.

Eating small meals and snacks every few hours can reduce your perception of fatigue because your brain needs a steady supply of nutrients.

Eat foods with a low glycemic index to help you avoid the lag in energy that typically occurs after eating quickly absorbed sugars or refined starches. Foods include whole grains, high-fiber vegetables, nuts, and healthy oils such as olive oil. Proteins and fats have glycemic indexes that are close to zero.

Having a cup of coffee can help sharpen your mind, but you have to use it judiciously.

Coffee can cause insomnia, especially when consumed in large amounts or after 2 p.m.

Avoid drinking alcohol at lunch. The sedative effect of alcohol is especially strong at midday. Avoid a five o'clock cocktail if you want to have energy in the evening.

If you're going to drink, do so when you don't mind having your energy wind down.

If your body is short of fluids, one of the first signs is a feeling of fatigue.