We spend around a third of our lives asleep, but the reason we sleep is still something of a mystery. Could it be the biggest mistake the evolutionary process has ever made? What does sleep actually do for us? David Edmonds meets Matthew Walker, one of the world’s leading sleep scientists, to discuss some of his findings. We’ll hear about how the clocks going back has an effect on heart attack rates, and consider why, if you’re struggling to sleep, the worst thing you could do would be to stay in bed.