you struggled to get out of bed this morning, scientists have come up with a handy excuse – you may be suffering from social jet lag.
They say sleeping in at the weekend can leave us too tired for the start of the working week, with many remaining groggy until Wednesday.
The immediate effects include poorer memory and reaction times, which would explain that familiar Monday morning feeling of sluggishness.
Over time, repeated changes to sleep patterns can also make you fatter and more likely to turn to cigarettes and caffeine, research shows.
The study at Rush University in Chicago into how changes in sleeping patterns affect reaction times suggests that a shift of just two hours can leave you worse off in the week.
Test subjects were asked to hit a button when they saw a bullseye appear on a screen, the journal Applied Ergonomics reports.
Unsurprisingly, they were slower in the mornings than in the evenings – but they were also far slower after a pattern of sleep similar to getting up early on a Monday morning after a weekend of late starts.
Lead researcher Helen Burgess said: ‘The weekend sleep in is just the process by which people shift their clocks later - it wouldn’t be a problem except for that rude awakening on monday morning when all of a sudden we need to shift earlier.’
The phrase ‘social jet-lag’ was coined by German researcher Till Roenneberg who has shown that the phenomenon can take a hefty toll on health, by raising the odds of drinking, smoking and relying on caffeinated drinks.
While travel-induced jet lag is something most of us only endure occasionally, social jet-lag can make itself felt every week.
His latest study, of 65,000 men and women, found that those with different weekday and weekend sleeping schedules were more than three times as likely to be overweight as those who tended to keep similar hours day after day.