You’ve just finished eating lunch and you’re back at your desk, ready to dive into the rest of the day’s work. Yet by 3pm, you find your eyes starting to droop. Before long, the only thing you can think about is how much you’d like to take a nap.

The “afternoon slump” (also sometimes called the “3pm slump”) is a common experience. It’s that distinct drop in energy that tends to occur in the mid-afternoon hours.

While it’s tempting to blame this sudden urge to snooze on what you’ve eaten for lunch, this alone can’t take the blame. The afternoon slump is actually caused by several distinct biological pressures beginning to converge.

One part of the explanation begins long before lunch. From the moment we wake up, our drive to sleep gradually increases. Adenosine – an organic compound involved in regulating sleep and wakefulness – accumulates in the brain while we’re awake, contributing to our gradual need to sleep, referred to as “sleep pressure”.

Yet the reason we do not simply become progressively sleepier from breakfast onwards is because another system is working alongside it. Our circadian clock, which controls our body’s sleep-wake system, generates a changing drive for wakefulness across the day.

During the morning, this system helps to counteract increasing sleep pressure. But in the early afternoon, we enter a natural period of increased sleep propensity. As sleep pressure has continued to build regardless, this........

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