Answer: In the six days of creation G-d created many things. The very first of His creations was light and darkness - day and night. We can understand why light - day was a necessary component of creation but why did G-d deem it necessary to create night as well? Our sages tell us that if G-d had not created the concept of night and if life would be just one long continuous day there would never be new beginnings in our lives. We would never appreciate the concept of turning over a new leaf and stating anew. At the very outset G-d wanted us to realise that just as every day is new and independent of the preceding one, so too we are given the opportunity to constantly start afresh and make new beginnings in our own lives.
Part and parcel of being human is that we are not perfect. But by creating the world with the concept of night and by fashioning us with the need for sleep, G-d is teaching us that though yesterday may have been less than perfect, nevertheless He still trusts us and gives us the ability to start on a new page today - a day that is brand new and totally independent of yesterday. Sleep teaches us that we have it within our power to recreate ourselves and start afresh.
For this reason the very first words one should say upon rising in the morning are the words of the "Modeh Ani" where we offer thanks to G-d for returning our rejuvenated souls to us and giving us the gift of life. As part of these words we also thank G-d for his faith in our ability to make today a better one than yesterday.
So sleep well and wake up a changed person tomorrow.