Recently I stayed at a friend’s house. “You snored all night long. It woke me up and I couldn’t get back to sleep for over an hour,” she told me the following morning. “Wake me up if it happens again tonight,” I said. “Did I snore last night?” I asked the morning after, although I had slept all night without being woken. “No, not at all. I don’t understand why,” she answered. “I told myself not to lie on my back at any point during the night, and instead only to move from my left side to my right side.”