Sleep is one of Allah's Divine Signs:

Dr. Rateb: 

In the Name of Allah, the Most Gracious, the Most Merciful. Praise be to Allah, the Lord of the Worlds, and peace and blessings be upon our Master Muhammad, the faithful and the honest.   

Once, a noble brother visited me at my office in Damascus. He had a problem I had never heard about before. He said, "I never sleep."  He swore to Allah that he was ready to pay a million S.P. to be able to sleep one night. 

He was suffering from a rare disease that prevents him from sleeping. He was ready to pay a million S.P. just to sleep for one night. Yes, there is such a disease but we got used to blessings that we no longer notice them.

Pay attention to the following Prophetic duaa’: 

(O Allah, let us consider Your Blessings when we have them, and not when we are deprived of them.)      

It is a great blessing to be able to sleep once you put your head on the pillow. Sleep is a very complicated process, during which the neurons get far from one another, so the neural pathway is cut. 

It is just like a wide rivulet that separates two banks that one cannot pass it. Hence, the neurons are far from one another during sleep so the neural pathway stops, and this is why man does not hear the voices around him. However, there are loud voices that force man to hear them.

Man is also forced to jump over a rivulet even if it is a wide one when he is chased by an enemy. Thus, his fear pushes him to jump.  On the other hand, when neurons are close to each other man stays awake.

As for voices, there are certain loud voices that wake man up upon hearing them, whereas he remains asleep when he hears the voices he is familiar with. Oddly enough, man's sense of hearing is selective. In an experiment, a tape recorder was put beside a window while two men were discussing things for an hour, and after they finished their conversation, they were asked, "What kind of voices and sounds did you hear from your surroundings?" They did not mention anything about it. When they listened to the recorder again there were nany sounds, such as the sound of the car crush,

the sound of the policeman's whistle, and many other sounds. This is amazing! Due to Allah's Perfect creation of man, man does not see or hear except the things he concentrates on, and he forgets about other irrelevant things.

When man focuses on something, he remembers it in details. The same applies for memory, imagination, and past information.  There is a difference between things you focus on and things you are used to.

There are smart things that you are used to like knowing the way to your house while driving back home without thinking a lot or noticing the streets. You pass way after way and take the right or left turn while driving without thinking as these are habitual activities. If we had to think about everything we do, our lives would have been so hard. However, there are complicated things that become super easy with frequency, and this is one of the Blessings of Allah.

When man intends to know Allah, Exalted and Sublime be He, attentively, he understands things deeply.

Dr. Bilal: 

Dear noble Ustaz, Allah the Almighty says: 

(And among his Sings is the sleep you take by night…)

[Ar-Rum, 23]

You mentioned the mechanism of sleeping, but sometimes some people sleep deeply while others sleep lightly.  

Allah's Wisdom behind deep and light sleep: 

Dr. Rateb:

It was said that Man sleeps deeply for two or three hours. When you are in the light sleep you can hear when one gets into your room, when someone is talking, or when a child is crying. 

On the other hand, when you are sleeping deeply, you don’t feel or hear anything. Nevertheless, due to Allah's Wisdom, while sleeping deeply, a mother may not wake up upon hearing a loud voice, but she hears the voice of her infant even if he sleeps in another room.

This is an exceptional case that is related to mothers; no matter how deep her sleep is, the voice of her infant can wake her up, because it is the most important voice for her, while other sounds that are much louder than his might not wake her up. This is how amazingly man is designed! 

Changing  positions while sleeping indicates Allah's Greatness:

Dr. Bilal:
 Dear sir, man changes his position while sleeping. Allah the Almighty says: 

(And We turned them…)

[Al-Kahf, 18]

Dr. Rateb: 

This is incredible. When man sleeps, his skeleton and the muscles that cover it press on the organs that are under the skeleton. The weight of the skeleton and the muscles make blood vessels narrow as pressure is applied to the body while sleeping on one side. As a result, man could feel one of his limbs numb.   

 (And We turned them…)

[Al-Kahf, 18]

The process of changing position is stunning in the sense that Allah the Almighty has created centers of pressure in man's body. For example, when man lies on his back the weight of his body affects his skeleton and muscles, so the cells under the skeleton feel the pressure and send a signal to the brain in order to change man's position. 
This happens even if man is sleeping deeply. Can you imagine that a sleeping man changes his position about forty or fifty times during one night? Allah the Almighty says:      

(And We turned them…)

[Al-Kahf, 18] 

This is due to the Greatness of Allah, Exalted and Sublime be He:

(And We turned them on their right and on their left sides…)

[Al-Kahf, 18] 

Turning on one side would can man to fall down from his bed. 

In conclusion, man's sleep is one of the Divine Signs that indicate Allah's Greatness.