I had bought this book but hadn't really paid attention to it -- bought it for one thing, found that, then put it on my medical reference shelf. Then a friend started having a sleep disorder that was really ruining his life. He went to one sleep specialist who put him on a medication for which even the pharmacist thought she had prescribed an awfully large dosage, and it didn't help that much, so she sent him to another specialist, who recommended a light box in the morning. He bought the thing, but thought it was kind of nutty, and after I set it up for him I came home and looked in this book and found a whole section explaining various forms of sleep disorder, with three or four possible explanations for his, including why and how the light box might work. I also realized that he and his wife do not close the blinds in their bedroom, which is a factor I don't think they ever considered. So I am buying a second copy of the book for them. What doctors fail to do, so often, is explain why they are doing something -- or explain it skimpily, or you can't take in what they do say because you are hearing new information that sounds weird...whatever, I know the explanations in this book are going to be useful to my friend, and now I will look through the other sections to see what else is there. Thank you, Smolensky and Lamberg.