Sunday night, Monday morning

It's Sunday night and it's twenty past eleven and you're not asleep. You went up at half past ten because it's a school night, and you've been lying there since, and the more you think about needing to sleep the less it happens. You've checked the phone twice. You've done the arithmetic about how many hours you'll get if you drop off now, and then again five minutes later with a smaller number. At some point you go, and at half past six the alarm goes off in what feels like the middle of the night, and you get up feeling thick and slow and slightly sick, and you stay that way until about eleven, and Monday is a day you get through rather than have.

Rewind to Friday. You were tired on Friday. You'd had five nights of half past six and five days of work, and you were running on coffee by Thursday afternoon, and by Friday evening you were on the sofa with a glass of something, and the one thing you were looking forward to was not setting the alarm. Saturday you woke at half past nine, and lay there another half hour because you could. Saturday night was a late one because there was no reason for it not to be. Sunday you woke at ten and felt, for the first time all week, properly rested. You had a slow breakfast. It was lovely. And then it was Sunday night and twenty past eleven and you weren't asleep.

These details are invented, but I'd guess yours are close. Some words. The short week is the five weekday nights on which you sleep less than you need. The lie-in is the weekend morning you sleep past your weekday time, and the late night is its partner, the Friday or Saturday you go to bed later because you can. The drift is what the lie-in and the late night do to your body clock, which chapter 4 is about, and which is measurable. The Monday is the state you're in on Monday morning, and often Tuesday too, and this book will argue that most of it is the drift and not the job. The Sunday-night wait is the lying awake. The wake time is the time you get up, and the method in this book turns on holding it steady. The window is the hour of slack the wake time is allowed at weekends. And the daylight walk is what happens within an hour of getting up on Saturday and Sunday, and chapter 16 says why.

Before you go on, do one thing. Write down what time you got up on each of the last seven days, as near as you can remember. Then write down what time you went to sleep, roughly. Look at the difference between the middle of your sleep on a weekday and the middle of it at the weekend. If it's more than an hour, this book is about you. If it's more than two, chapter 10 has something to tell you.