According to Brian Tracy, there are 3 forms of energy that a person has to be aware of:

Physical, Emotional and Mental Energy.

On a physical level, you want to be well-rested and fit. There is no way you are getting things done when you are physically tired. On an emotional level, you need to feel good and have positive emotions to bring out the best in yourself. When you are experiencing a storm of negative emotions it is very hard to focus and work at the task at hand. Lastly, on a mental level, you must have the desire and willpower to work.

These are interrelated and have to be recharged to live a successful life. People tend to consume their emotional energy by being negative. Nurturing negative emotions such as anger, disappointment and fear will burn you out. When this energy is consumed, physical and mental energy are also affected.

Successful people have an effective way of conserving their emotional energy. They are calm, objective in dealing with situations and able to control their emotions.

When you take physical relaxation, your emotional and mental batteries are recharged as well.

You have the most leverage to get work done when your physical, emotional, and mental energies are in sync. Start paying attention to your energy levels to be more productive. The goal in taking a rest and having relaxation is to build and use your energies to have a quality and successful life.