In the no-man's land between wakefulness and sleep, the ordinary rules of consciousness can break down. Dreams can spill into waking life, awareness can re-enter a dream, and the sleeping brain can awaken before the body. Sometimes cinematic visions of REM intrude into consciousness, like dreaming with your eyes open. People across the world report terrifying bedroom intruders: witches, demons, aliens, vampires, and even gigantic cats. Harvard neuroscientist Baland Jalal explains these apparitions as the brain's attempt to make sense of the impossible, filling in the gaps to construct a new reality until we awaken and it fades. One of the world's foremost researchers of sleep paralysis, he sees it as a window into the brain's wider functions. Yet sleep paralysis is only one of several remarkable states that emerge on the edge of sleep. By exploring it alongside lucid dreaming, narcolepsy, and REM sleep behaviour disorder, Jalal reveals how these unusual states illuminate the neural machinery of human nature.

Packed with fascinating stories from research that has taken him all around the world, he explains how our expectations and cultures shape the visions we bring to life, and what this might mean at the deepest level for who we are. How it is that the activity on such small scales within the brain gives rise to consciousness in all of its complexity, and our sense of the self, helping us understand what it means to be so uniquely human.