Mind & Psychology - 29 free documentaries about sleep & dreams.
Start with Confronting the Unknown: Inside the World of Sleep Paralysis Attacks (49 min, Real Stories), then The Strange Science of Why We Dream (15 min, Be Smart). All 29 documentaries here are free to watch from their makers' official uploads. To read deeper, the top-rated book on sleep & dreams is Why We Sleep by Matthew P. Walker.