An article on the Indian news site explains why Ayurvedic medicine recommends sleeping on the left side. 

According to Ayurveda, the left and right sides of your body are different and also behave differently. Interestingly, the theory that you should sleep on your left side for good health stems from the ancient and holistic science of Ayurveda. We all know the time quantity and quality of sleep we get each day matters, but so does the sleep position. Here are four health benefits that you can derive by sleeping on your left side.