Sleeping is something all of us do every day, but exactly what happens to us when we sleep isn’t completely understood. On today’s edition of Please Explain, we’re looking into why we sleep, why we sometimes can’t sleep, and why many of us aren’t sleeping enough. Dr. Allan Pack, Chief of the Division of Sleep Medicine and Professor of Medicine at the University of Pennsylvania, and Dr. Michel Cramer Bornemann, Co-Director of the Minnesota Regional Sleep Disorders Center at Hennepin County Medical Center in Minneapolis, join us.