We spend roughly a third of our lives in bed, but for millions of us, not all of that time is spent sleeping. We strive for eight hours per night, only to lie awake thanks to stress, our ever-present devices, a new baby, or that 4pm coffee you thought you needed. We’re hardly the first to experience this. When our ancestors evolved hundreds of thousands of years ago, saber-toothed tigers were their biggest nighttime worry, and wakefulness served to protect one’s tribe at night. They had no concept of sleep stress; their episodic sleep patterns gave them an evolutionary advantage.