What is the truth of sleep? Al-Khattabi said in Gharib al-Hadith : It is a heavy trance that attacks the heart and cuts it off from knowledge of outward matters . It was said a strange definition, which is : It is the flow of blood to the liver and its meeting in it is nothing but . It has been proven on the authority of the Prophet [ may God’s prayers and peace be upon him and his family ] that he said : Sleep is the brother of death, and the people of Paradise do not sleep . It was authenticated by al-Albani in al-Sahih  and at the present time there are [ several theories ] that tried to explain sleep, including : The vascular theory : sleep is explained by the lack of blood on the brain . Chemical theory : It says that sleep is the result of the effect of chemical reactions and metabolism, so toxic substances are formed in the blood that abound, pass to the brain and increase sleep . Pavlov’s Theory : Concerning Causation and Arousal . Ray Medes theory : He is a professor of humanities at the University of London, and he explained sleep usually, and says that a person is accustomed to sleep and therefore sleeps, and therefore if he gets used to leaving sleep little by little, he did not sleep at all, and remained awake . This disturbance or perplexity in the matter of sleep is with the one who does not believe in the unseen. As for the Muslim and the believer, he believes in what he came from God and His Messenger, because he knows that this is the truthful news to ensure knowledge, truthfulness, and the completeness of the statement, as the Almighty said [ Does he not know who is created and he is the kind and the expert ] ,,,, , So he believes in an outlined belief in what is more beautiful and detailed in what has been detailed, and entrusts knowledge to his world, and whether or not he realizes the method, and whether he knows the wisdom of the matter or not, and he obeys God and his wisdom, law and law, his state is what the angels said : [ Glory be to you we have no knowledge except what You taught us that You are the Knower, the Wise ]. Be aware that sleep is initially a perplexing matter in its attack on man and his control over him and severing this person’s relationship with the outside world, without the slightest will of man, and some wait for hours and do not come to him, and may come to him at a time when he does not want him, and some flee from bed and from sleep for fear of what he used to be Afflicts him and comes from nightmares or Jathoom .