This book illustrates several positions in which to place your body for sleeping. Its primary flaw is that once you fall asleep, you unconsciously shift your position such that you're no longer sleeping in the prescribed position. One experiment this book prompted for me was, after going to bed, to force myself to stay alert right up until the instant when sleep overtook me, so that I could ascertain more about the sleep process and understand what it entails. The problem is, I just could not do it -- I always fell asleep first. An improvement to subsequent editions of this book would be instructions on how to stay awake until you fall asleep.