We've nearly all been there at least once - awakened with a pounding heart and the memory of frightening scenes that seemed so real, but were conjured up and existed only in the sleeping mind. Nightmares affect people across countries and cultures, with some 10 percent of the world's population reporting recurrent nightmares. Parents have reported, and science has recorded, nightmares in children as young as 18 months old. Up to 40 percent of children aged 2 to 12 experience nightmares, as do some 35 percent of veterans and 50 percent of adults with chronic illness. With this book, a psychologist widely known in his field shows how nightmares evolved and were useful to ancestral populations, and why nightmares may carry beneficial functional effects even today for people who suffer from the pulse-pumping dreams. McNamara brings us up to date on the biology of nightmares and what, specifically, happens in the brain during the event. He also explains the history and development of nightmares and likely causes, including traumatic events, psychological and physical disorders, and commonly consumed medications.