Have you ever had a nightmare where you’re being chased by a monster, and woken up abruptly with your eyes wide, your lungs heaving and your heart racing? If so, you’ll fully understand how our bodies react to danger. Now imagine that you woke up outside, without any doors or walls to keep you safe, and there really was a monster – in fact, several of them – all around you in the dark. And they were there every night. Would you ever go to sleep again?