"It's always at night"

Look back at the history you checked in chapter 1 and you'll probably find that most of the long searches began after ten at night. There are some plain reasons for that, and they say something about how far to trust what you conclude at that hour.

The first is that night is when you notice your body. All day there's been something else to attend to. In bed, in the dark, lying still, there's nothing to compete with a twitch or a heartbeat or an ache. The sensation is probably no stronger than it was at three in the afternoon, when you were too busy to notice it. It gets your attention at night because there's nothing else to notice. This is my reasoning, though I doubt many people would dispute it.

The second is that night is when nobody can be asked. The surgery's closed, the pharmacist has gone home, and your partner's asleep. You might ring 111 for something that alarmed you, but for a fluttering calf you wouldn't think of it. So the phone seems like the only thing open. In the daytime the same worry has other places to go, and it often gets mentioned to someone or dealt with, or else forgotten.

The third is that you're at your worst at that hour. A group of sleep researchers led by Tubbs has put forward what they call the mind after midnight hypothesis. They brought together evidence that positive mood is at its lowest in the small hours and negative mood peaks then. The kind of thinking you need for weighing evidence and stopping yourself is also impaired when you're awake at a time your body expects to be asleep. They offer it as a hypothesis for further testing. Separately, Palmer and colleagues pooled 154 studies of sleep loss and found that people who were short of sleep felt less positive and more anxious. If you've had a bad fortnight of sleep, as you had in chapter 1, you start the search already more anxious than usual.

Put those together and the night-time search looks like this. You do it when sensations seem strongest and your mood is lowest. Your judgement is at its weakest, and the only source open to you is the one that leans towards alarm. Then you decide what the twitch means. The hour affects that decision at least as much as your calf does.

It's worth comparing how the same worry looks at different times. In chapter 1, by morning the fear had shrunk to a manageable size and you felt slightly foolish. Nothing about the twitch had changed overnight, but you were a different reader of it.

One rule follows from this, and it will come back in chapter 17. A new sensation noticed at night waits until morning, unless it could be an emergency. If it really does need a look, a four-minute look over breakfast will be calmer and more accurate than an hour at midnight. And a good share of what you notice at night won't be there in the morning to look up.