A productivity coach has explained why many of us feel tired in the middle of the afternoon. Watch here:
In the clip, she explains that it's all about the 'circadian pacemaker'.
She says: "We have rises and falls of hormones, body temperature and chemicals that fire in your body that typically reset - key word typically - on a 24-hour cycle.
"And studies have shown us that the daily high point and the daily low point of your brain have the performance effect of drinking the legal limit of alcohol."
So basically, you could have a couple of beers at your high point and still be as productive as you're likely to be in the mid-afternoon; tell that to your boss next time they complain about your 10am pint.
As part of our bodies' natural circadian rhythms, our core body temperature tends to drop between 2pm and 4pm, which in turn releases a hormone called melatonin which can make us feel drowsy.
For many people, this perfectly normal period of drowsiness can seem totally overwhelming and insurmountable - particularly if you have a tendency to exacerbate the situation with a heavy lunch.
But while the most appealing thing during such slumps might be a nice little nap, Dr Ian Katznelson, neurologist at Northwestern Medicine Lake Forest Hospital in Illinois, advises that you do the exact opposite.
He said: "There are many reasons why people feel less energetic in the afternoon, especially between 1 and 4pm. In part, it's physiological: our normal circadian cycle dictates a period of sleepiness or decreased alertness in the afternoon.
"However, sleep disorders, medical disorders, stress, insufficient sleep or poor eating habits can also cause excessive sleepiness at this time. Maintaining consistent sleep schedules, even on the weekends, will help your energy levels throughout the day.
"If you experience an excessive mid-day slump, think twice before reaching for empty afternoon calories or taking a power nap, which can interrupt your normal sleep patterns.
"Instead, get up and move around, preferably outside, to get your blood and oxygen pumping, reduce tension and boost your vitamin D from the natural light. Make sure you're drinking enough water because dehydration can cause fatigue.
"And, if you are really hungry, opt for a protein-based, energy-boosting snack such as lean chicken or a handful of almonds."
If you feel as though your tiredness is more than simply circadian rhythms doing, it is worth investigating whether you could be experiencing fatigue for some other reason.
You can learn about 10 medical reasons why you might feel tired here.