Are you a weight lifter, pumping iron? As you lift weights, certain nutrients are depleted in your muscles and nerves. Even the best weight lifters - or workers in general - must relax and replenish the lost nutrients to be able to continue working. This kind of replenishment is NOT about sleep. You don't absolutely require sleep to rebuild lost muscle fatigue. You can do it simply by resting. So what is sleep replenishing.

To say it in simple terms, sleep replenishes the nutrients lost, in the brain, from the decision-making process. Normally, in every-day life, a person makes thousands of decisions. Many of the decisions involve a series of decision/counter-decision brain activities, especially where some form of stress is involved. Sleep relaxes the decision-making process so that nutrients can be restored to the brain's decision-making centers. Dreams are part of the process that the brain uses to analyze and direct the nutrients to the places in the brain where they are most needed.

The "visions" we see in dreams are often incidental... often revolving around some stressful operation done while awake... because that's where the brain is replacing large amounts of nutrients while we are sleeping.