What is the right way to sleep?

 When man goes to bed, he should see on which side he lies. People lie on their abdomens, backs, left sides, or right sides. Those who lie on their abdomens feel difficulty in breathing, as their backs and skeletons weigh heavily on their lungs. Besides, such type of lying is improper and inadequate.
 Those who lie on their backs prevent the work of a very important mechanism of their body, namely that of warming and filtration of the air coming into the lungs. In the human nose there are interlocking surfaces with muscular arteries. When these muscles expand, they allow a great amount of blood to flow through the arteries. And when the air passes along these interlocking surfaces and touches the great amount of blood flowing into the nose, it becomes warm and reaches the trachea while its temperature is 38 degrees Celsius, even if its temperature before getting into the nose were zero degrees Celsius. Besides, The interlocking surfaces have a sticky substance that attracts the dust, soot or smut carried by the air. If anything escapes the interlocking surfaces, there are the hairs that Allah, Most Gracious, created inside the nose in order to catch alien bodies and prevent them from getting into the lungs. It is indeed a most efficient warming and filtering mechanism that enables the air to get to the trachea filtered, warm, clean, pure and fresh.
 If man sleeps on his back and breathes from his mouth, he stops the work of this highly complicated mechanism as mentioned above. Moreover, in the cold the nose becomes red as much more blood is made to flow into the nose. If man breathes from his mouth, what happens? He becomes more liable to colds, his gum gets dry and retarded, and his snoring becomes unbearable. Sleeping on the back and breathing through the mouth cause all of this.
 Therefore, sleeping on the abdomen or the back is improper. But what about sleeping on the left side of the body? Food usually needs 2-4 hours to be digested, but if man sleeps on the left side of his body, digestion needs 5-8 hours. This is because the right lung, which is the bigger one, presses on the heart, while the liver, which is the biggest organ of the body, remains hanging and unbalanced. If, however, man sleeps on the right side of his body, the left lung, which is the smaller and the lighter one, the liver becomes stable towards the earth and digestion becomes faster. In this context, Abu Hurairah, the venerable Companion, may Allah be pleased with him, said, “Allah’s Messenger, (PBUH), once saw a man lying on his abdomen. He, (PBUH), said,

“Allah does not like such way of lying.”

[Narrated by At-Tirmithi (2768) and Ahmad (8028)]

A prophetic Hadith confirming on the right way of sleeping:

 The prophet (PBUH) said:

'Whenever you go to bed, do wudu’ as you do wudu for the prayer and then lie down on your right side. Then say: 'O Allah, I turn my face to You and I entrust my affair to You.’”

 It has been said: “Sleep on the back is that of kings; sleep on the abdomen is that of devils; sleep on the left side is that of the wealthy - for they eat a lot; and sleep on the right side is that of the knowledgeable and wise.”