Why the mind clocks on

If you lie awake working through problems, you may have concluded that you're a worrier, or that you can't cope, or that your life is more of a mess than other people's. I don't think any of that follows. The night shift has real attractions, and they'd pull at anybody.

The first is that the problems are real. The roof does leak, and your mother is having an operation. The night shift doesn't invent its material. It takes genuine unfinished business and works on it, and that's why it's so hard to dismiss. Telling yourself not to be silly doesn't help, since thinking about a four-thousand-pound bill isn't silly.

The second is that it's the first quiet you've had all day. From the moment you got up there were people and screens and tasks. Nobody is asking you for anything at three in the morning. For many busy people it's the only stretch of the day with no interruptions, and the mind takes the chance to raise everything it couldn't get a hearing for earlier. I think this is a large part of it. I'll come back to it in chapter 11, because it points towards the remedy.

The third is that it feels responsible. Lying in the dark with a problem and refusing to think about it seems like negligence. Working on it seems like the conscientious thing to do, a sign that you take your obligations seriously. People who do the night shift are very often the people who hold things together for a family or a team by day.

The fourth is that it feels like a good use of dead time. You're awake anyway, and you might as well get something done.

The fifth is a promise. It seems that if you could only get this one thing straight in your head, your mind would let you go back to sleep. So you work at it with some urgency, as though it were the price of rest.

Allison Harvey, a psychologist who studies sleep, put thinking of this kind at the centre of an influential account of why insomnia persists. In her model, people who sleep badly tend to have a great deal of worried mental activity in bed, and part of what keeps it going is a set of beliefs about it. One of those is the belief that worrying in bed is useful. Her paper is a theory, drawing on clinical work and earlier studies. It's about people with insomnia, which you may or may not have. But the observation carries over. People keep doing the night shift partly because they believe it's useful work.

Underneath these attractions are needs nobody should be ashamed of. You want your problems dealt with. You want to be someone who doesn't let things slide. You want some time in the day that's quiet enough to think. And at that moment you want, very badly, to go back to sleep. The question for the next several chapters is whether the night shift serves any of those. I'll argue that it fails all four, and that the last one is where it fails worst.