Sleeping on your belly is bad for your respiratory system. Your breathing is also limited. Your back is pressing your chest against the bed and preventing proper contractions. The respiratory problems would lead to other shit.
Plus, if your using a pillow then your neck vertabrates would be in an unnatural position. meaning it would lead to problems with your posture in that area.
Lying on your back is also an unnatural position, as your inferior jaws would relax and lead to breathing through the mouth. This leads to drying of the gums and inflammations associated with that. The air that you would breath wouldn't be as purified as it would be if you breathed through your mouth, as the nose contains hair and mucous to clean the crap out of the air. There are other conditions associated with lying on your back in sleep. It prevents the easy flow of breath through your repiratory system, hence snorig will increase.
Sleeping on the left side is problematic also, as the heart would be then under the pressure of the right lung, the biggest of the two lungs, and this would affect its contraction especially if the person is old. The full stomach which itself is under the pressure of the heaviest organ in your system, the liver, which delays its emptying cycle, would also impose a pressure on the heart.
sleeping on the right side is the best possible position, as the left lung is smaller than the right one and the pressure on the heart would therefore be less the heart would perform its function better, the liver would not be suspended, and the stomach would be on it and so emptying its contents would be quicker. There are other more detailed benefits of sleeping on your right hand side.
