The world is messing with our minds. Rates of stress and anxiety are rising. A fast, nervous planet is creating fast and nervous lives. We are more connected, yet feel more alone. And we are encouraged to worry about everything from world politics to our body mass index. Matt Haig talks to Brigid Delaney about how to stay sane on a planet that makes us mad. How do we stay human, in a technological world? How do we feel happy, when we are encouraged to be anxious?