People spend about one-third of their lives asleep, but what actually happens when we close our eyes and begin to dream? For this week’s Please Explain we are joined by Wallace Mendelson to better help us understand. Mendelson is the former director of the Sleep Research Laboratory at the University of Chicago and author of the new book The Science of Sleep: What It Is, How It Works, and Why It Matters. He tell us about the different stages of sleep, sleeping disorders and how outside forces like alcohol and sleeping pills affect our rest.