hello i hope your doing well a rebbe gave me advice without reasoning behind it he said you should sleep on your left side and then later on that night sleep on your right do you know why?

Shalom, Thank you for your question. The issue of which side to sleep on is addressed by our Rabbis – however, before answering your question, let me point out that this is not an obligation, but rather good advice. So, if it is difficult, or for any other reason a person does not follow these directives or which side to sleep on, they shouldn’t worry. In the classic work “Kitzor Shulchan Aruch” (The Concise Code of Jewish Law) by Rav Ganzfreid z”l, he writes (Chapter 71, law 5) “It is advisable to begin sleeping on the left side and finish on the right side; this is beneficial for one's health because the liver is located on the right side and the stomach on the left, and when leaning on the left the liver rests on the stomach and warms it with its heat thereby facilitating the speedy digestion of food. After the food has been digested it is advisable to turn on the right side so that the stomach rests and cause the waste to pass, and you should not turn from side to side too often [during the night]”. I hope this is of some help to you, Blessings.