The Prophet (Sallallahu Alaihi wa Sallam) ordered us not to sleep on our bellies (face down). Abu Dawood reported from Yaesh that Takhfa al-Ghafari said: “My father said ‘while I was lying on my belly in the mosque I felt a person moving me with his foot saying: “Allah hates this way of lying down” I looked up to find out that (the man who was speaking) was the Prophet (Sallallahu Alaihi wa Sallam)” .
Some scholars state that it is dislikable to sleep on the belly.
Al-Tirmizi also reported from Abu Hurairah that he said: “The Prophet (Sallallahu Alaihi wa Sallam) saw a man lying on his belly he said to him: Allah does not like this form of lying down” . Ibn Majah reported from Abu Zar : “This is the way in which the dwellers of Hell-fire lie down” .
Ibn al-Qayyim said while talking about the medicine of the Prophet (p.b.u.h.): ‘The best is to lie on the right side as this makes the food rest more comfortably in the stomach because the latter is inclined to the left. Then it is better to change to the left side as this makes the food get digested more quickly. But most sleeping should be on the right side… And it is bad to sleep on the back. But it is worse to sleep face down on the belly’ .
So, sleeping on the belly is dislikable and can be harmful to health.

Rest Allah knows the best

SCIENTIFIC facts:

It’s best to sleep on your right side, because your liver is your heaviest organ and if you sleep on your left then it will cause you discomfort, because it’s squishing your stomach.

sleeping on the right/ left side with the hand under the cheek:
1. organizes the heart pulses.
2. permits the sleeper / asleep person to breath in very natural, perfect way.

but who sleeps on his tummy, suffers the following:
1. temporal dyspnea
2. his neck’s vertebra get harmed and will have pains on the long term.