"But the problems are real"

They are. I said so in chapter 2, and nothing since has changed it. The roof leaks, your mother needs looking after, and work is uncertain. A book that told you to breathe deeply and think of a beach would be insulting, because your problems wouldn't be any smaller when you opened your eyes.

So the argument of this book isn't that you should think about your problems less. You should think about them at a better time, and until you do, the night shift will keep happening. Here's why I believe that.

Go back to the second attraction in chapter 2. Three in the morning is the first quiet you've had all day. Consider an ordinary day from your mind's point of view. There's the rush of the morning, then work, with its own demands, then the evening's cooking and clearing and children, then a screen, then bed. At no point in that day did you sit down for ten minutes and ask yourself what's outstanding and what you're going to do about it. The questions about the roof and your mother and your son were there all day, waiting, and they never got a turn.

At three in the morning they finally get one, because nothing else is competing. Seen this way, the night shift isn't a malfunction. Your mind is doing a necessary job at the only time you've left free for it. The job is the review of open problems. It has to be done at some point, and if you don't schedule it, it gets done in the small hours.

This suggests a remedy, and there's evidence for it.

Colleen Carney and William Waters tested a procedure they called constructive worry. They recruited 33 students who reported insomnia. After two nights of baseline measurement, the students were split into two groups for five nights. In the early evening, one group wrote down the problems that were likely to bother them that night, along with a possible next step for each. The other group wrote down their worries and filled in questionnaires about them. The group who'd written next steps reported less mental arousal in bed than the comparison group, and less than they'd had at baseline. It was a small study and a short one, and the participants were students. The difference between the two groups is still instructive. Both groups had listed their worries. Only the group who'd added a next step to each one had quieter nights.

Michael Scullin and colleagues ran a related experiment in a sleep laboratory, with 57 healthy young adults. Before lights out, each spent five minutes writing. Half wrote a to-do list of things they needed to get done over the next few days. The other half wrote about things they'd already completed. Sleep was measured with electrodes and not by asking people how they'd slept. The to-do list group fell asleep significantly faster. The more specific their lists were, the faster they fell asleep. That was one night, in young people without sleep problems, and what was measured was falling asleep at bedtime and not returning to sleep at three. I wouldn't rest a great deal on it. It does point the same way as the first study.

Research on unfinished tasks in general points the same way. Psychologists have found that an unfulfilled goal keeps intruding on the mind, and that making a specific plan for it quiets the intrusions even though the goal remains unfulfilled. Your mind seems to be less concerned that the problem is solved than that it's in hand. The NHS guidance on sleep makes a plainer version of the same suggestion. If you often worry in bed, it says, try making a list of things you need to do the next day before you go to sleep.

The reasoning that links these is mine, though it's hardly original. Your mind raises problems at night because it has no assurance that they'll be dealt with otherwise. The way to give it that assurance is to show it, every evening, that each problem has been written down and has a next step and a time. After a week or two of this, when the roof comes up at three, you'll be able to give a truthful answer. "It's on the list. I'm ringing the roofer at lunchtime." An answer like that does far more to let your mind go back to sleep than any amount of further thinking would.