Every day is a cycle of beginnning to end. Sleep resets the system, rejuvinates and restores, and all that has gone before is seemingly forgotten upon waking before slowing trickling back into consciousness.
     One could be said to have 'died' to the world in the interim. The world kept turning during this interval but you did not stir, or maybe you did, but your awareness of your surroundings was certainly less.
     So what?

     This is a big deal. Sleep takes you off the stage for awhile. It is nature's built in cooling-off period. You haven't been on the bridge steering the ship then you wake up to find things have changed. Now you have to adjust.
     Things have changed in your body. You might feel recharged or you might feel that the rest you got was insufficient and you are feeling kind of hazy, still 'not there'. You probably are having different thoughts about an issue, or no thoughts at all. You might be feeling elated by a dream you've had, or bummed out, sensing excitement about the upcoming day, or be plagued by some vague foreboding.

       The cycle of the new day has begun. It will run its course, like the thousands of days that have come before, and at the end of this one you will once again be irresistibly called back to bed. Nobody can continue to stay awake for very long. This built-in timer is an absolutely necessary biological shutdown. Studies have shown that sleep-deprived individuals become increasingly irrational and hallucinatory. What a curious thing! No matter how much technology humans develop, the need to sleep will still remain, stealing away thirty percent of your life with its unreasonable and quite unproductive demand of your time.

    "Hmmph!"  

    But, nothing you can do about it.
    So why? Why is this state called sleep necessary?
     No one knows. Humans seem to need an extraordinary amount of maintenance in this regard. We, the only self-aware, thinking species, should have conquered this 'problem' long ago because time is the ego's enemy. More time is required! I must have more experience!
   "Not!" says The Universe.

     "Why?"