Social Jetlag: Why Monday Morning Feels Like a Flight

Daniel sets his alarm for 6:15 on weekdays. On Saturday he sleeps until ten, because he finally can. Then he sits over his Monday coffee feeling like someone who has just stepped off a transatlantic flight, even though he spent the last forty-eight hours at home.

That feeling is not laziness and it is not the end-of-weekend blues. It is a measurable shift of the internal clock, and you inflict it on yourself by living on one schedule for two days a week and a different one for the other five. The technical name for it is social jetlag, and to some degree it applies to most working adults.

Two clocks that drift apart

The chronobiologists Till Roenneberg and Marc Wittmann introduced the term in 2006. They used it for the gap between two kinds of time that rarely keep step with each other. Biological time says when the body would sleep if nobody woke it. Social time is set by work, school, the nursery opening hours and the departure board at the station.

You can work the gap out on the back of an envelope. All you need is your mid-sleep point, the moment exactly halfway between falling asleep and waking up. On a working night Daniel drops off around half past eleven and gets up at 6:15, which puts his mid-sleep at roughly three in the morning. At the weekend he falls asleep after midnight and sleeps until ten, which pushes the midpoint to five. Those two hours are his personal dose of social jetlag.

Roenneberg later collected sleep data from tens of thousands of people, and a gap of at least an hour turned out to be the majority experience. A smaller but far from negligible group sits higher, around two hours and beyond. So this is not a quirk of a few night owls, it is the normal condition of an adult with fixed working hours.

The simplest way to notice that your two clocks have parted company is the alarm. Wake up on Saturday on your own, at roughly the same time as on Tuesday, and your biology and your schedule are in agreement. Sleep two hours past your usual time with no alarm, and you have been running a debt all week that the body collects at the first opportunity. An alarm cannot wake you at a suitable point in the sleep cycle, only at the scheduled one.

Now the comparison that makes the term work so well. On Friday evening you push your bedtime an hour or two later and on Saturday you get up later still. The internal clock reads this much as it would a flight across a few time zones heading west. On Sunday night you board the return leg, eastward, which is the nastier half of any trip. There is no airport and no suitcase involved, but the Monday fog is entirely real.

Why sleeping in does not clear the debt

Weekend catch-up sleep is not pointless. Part of the shortfall genuinely can be made up, and after a Saturday spent in bed until ten you do feel better than you did after five mornings of getting up in the dark.

The trouble is what happens to the timing in the meantime. The internal clock is set mainly by the light that reaches the retina in the first hours after waking. If the blinds stay shut until ten on Saturday, the brain gets the message that morning now starts later, and it moves the evening accordingly. Melatonin, the hormone whose level rises in the evening and accompanies the onset of sleep, is released later too.

Sunday night is then the scene almost everyone recognises. You are lying in bed, you know the alarm goes at six, and you are wide awake. It need not be Monday anxiety, though anxiety is happy to join in. The body simply is not ready for sleep yet, because two days were enough for it to learn a later start to the night.

So Monday morning takes not one hit but two. On top of a short night comes the fact that at 6:15 the body is biologically somewhere in the middle of the night. Hence the cotton-wool head that two coffees will not fix. Caffeine masks the sleepiness, it does not reset the clock.

What is most awkward about the Monday fog is how easily it gets underestimated. You get used to the dulled alertness over the course of the morning and stop registering it, but attention and decision speed do not come back merely because they have stopped complaining. A difficult negotiation, or a decision that is expensive to reverse, is a poor fit for a Monday morning. If it can be moved to Tuesday, that is worth a try.

It is worth adding that social jetlag does not stop at your Monday mood. Roenneberg's team later described a link between a bigger rhythm gap and higher body weight. That is a statistical association rather than proof of cause, but it fits what people know from their own kitchens: after a broken Sunday night, buttered toast appeals more than porridge.

Who gets the worst of it

Social jetlag is not handed out fairly. The worst off tend to be evening types, the owls, who are expected at a desk by eight. Their bodies would naturally fall asleep around one and wake around nine, and the timetable says otherwise. So they sleep less than they need during the week and make up the deficit at the weekend more dramatically than anyone else.

Morning types have the opposite deal. A lark finds that a natural rhythm and standard office hours line up rather well, gets up at seven on Saturday too, and ends the week with a quarter of an hour of difference between working and free days. Social jetlag is therefore something a lark barely recognises and honestly cannot see what the fuss is about. Doves in the middle of the axis land somewhere in between.

The second deciding factor is how stable your rhythm is. Some people run on a steady rhythm, so a one-hour shift knocks them sideways for several days. Others run on a flexible rhythm, adjust within a day and show no sign of the same shift at all. Two people with an identical two-hour gap can have completely different Mondays.

Age matters too. Work by Mary Carskadon and other chronobiologists showed that the internal clock moves to later hours during puberty and only drifts back towards an earlier setting some time after twenty. A teenager who is not sleepy at one in the morning is usually not being provocative. Their biology is somewhere other than the school bell, and once you add a first lesson at eight, social jetlag appears at precisely the age when sleep matters most.

A rough guide to how gaps of different sizes tend to show up:

Before you read on, put the question to yourself in concrete terms: how many hours apart are your mid-sleep points on a working day and at the weekend? A rough estimate from the last fortnight will do. Most people have never worked the number out, and it usually comes in higher than they expected.

Where you sit on the axis between lark and owl is covered in more detail in the guide to chronotypes. If you are not sure, a short chronotype test will place you on both axes in a few minutes.

How to shrink the gap without losing your weekend

The advice to get up at the same time on Saturday as you do for work is technically correct and practically useless. Almost nobody keeps it up beyond three weeks, and time off has a job to do as well. The version that works is milder and cuts the gap roughly in half.

• Sleep in, but with a ceiling. One extra hour compared with your working wake-up reduces the debt and barely moves the clock.
• Light straight after waking does more than any alarm. Ten to twenty minutes outdoors, even under cloud, gives the body an unambiguous signal about when the day began.
• Morning movement reinforces that signal. It does not have to be training, walking to the bakery counts.
• When the urge to catch up is genuinely strong, a short afternoon nap beats sleeping until noon. Twenty minutes, taken by about three o'clock, reduces the tiredness without wrecking your bedtime.
• On Friday, watch the evening rather than the morning. Pushing your bedtime by two hours is where the whole problem starts, and Saturday's lie-in only follows from it.
• Sunday morning is the lever on the whole of Monday. Get up closer to your working time, get outside before noon, and you will fall asleep earlier that night.

What does not work deserves a mention too. Long weekend sleep as a substitute for habitually short nights is a fix that breaks itself every week, because it leaves the cause exactly where it was. If you could pull an extra half hour out of those five working nights, the need to catch up falls, and so does the size of the Monday hit.

A practical note for anyone with flexible hours at work: for an owl, starting half an hour later does more than any evening routine ever will. The internal clock is hard to talk round, whereas a calendar can occasionally be persuaded.

Clock changes and the sleep there is not enough of

Social jetlag cannot be dealt with in isolation, because it adds to two other things. The first is the spring shift to summer time, which takes an hour off everybody and works like an extra dose of jetlag applied to a whole country at once. Anyone already carrying a two-hour weekend gap adds another hour on top, and the March Monday is rough. What the transition does to the body, and how to make it easier, is covered in the piece on the clock change.

The second is your total sleep need. Social jetlag is a question of timing, chronic sleep loss is a question of quantity, and each makes the other worse. When you sleep enough, a one-hour shift throws you less than it does when you have been running on seven hours instead of eight for months. How much sleep is actually enough, and why the answer differs from person to person, has a piece of its own on how much sleep you need.

Monday is decided on Sunday morning

Daniel sorted it out in the end without any heroic resolutions. He kept the Saturday lie-in until nine, but on Sunday he set the alarm for eight. He had breakfast on the balcony and took the dog out for an hour before noon. His Sunday evening moved forward by about an hour, and the Monday fog shrank from the whole morning to the first hour at work.

Most people instinctively attack Sunday evening instead. They go to bed early, count sheep and get nowhere. The decision was made a day and a half earlier, on Saturday morning behind closed blinds. If you want a functioning Monday, watch one thing next weekend: when you first see daylight.