Personal experience: undetermined, possibly posture- or prediabetes- related reasons led to myself dehydrating at 10 times the normal rate when sleeping on any of the sides, starting at about age 27. As such: enjoy the variety while it lasts (left side is usually mentioned as more optimal of the two because of the way the liquids in the digestive system are positioned). Learning to sleep on the back did not take much time or effort at all.
Personal experience: undetermined, possibly posture- or prediabetes- related reasons led to myself dehydrating at 10 times the normal rate when sleeping on any of the sides, starting at about age 27. As such: enjoy the variety while it lasts (left side is usually mentioned as more optimal of the two because of the way the liquids in the digestive system are positioned). Learning to sleep on the back did not take much time or effort at all.