It saves your liver from overloading
Since the liver is on the right side of the body, lying on your right side can put a strain on this organ. The left-side sleeping position, however, won’t allow the toxins and other harmful substances to overload your liver.
It is good for your heart
The left side of the heart receives blood from the lungs and pumps it out to the body. Therefore, a left-sided sleeping position may help your heart to do its job more easily and efficiently. When you sleep on your left side, gravity facilitates the function of your circulatory system, especially your aorta and inferior vena cava, a large vein that carries de-oxygenated blood from the lower body to the heart and lies on the right side of your spine.