Your weekend lie-in might seem like a good idea at the time, but if you’ve ever woken up after a big sleep feeling even groggier than before you went to bed, you’ll know it’s not always for the best.

So why does this happen? Rebecca Robbins, a sleep researcher at Harvard Medical School and co-author of Sleep for Success, tells HuffPost UK it’s because we’re throwing our systems out of sync.

Our bodies are creatures of habit, she explains. The circadian rhythm relies on structure, including: exposure to light first thing, keeping a consistent sleep schedule, and adopting bed-time patterns that tell your body you’re gearing up for sleep. 

To put it simply: we love a good routine, so when we sleep past our usual wake-up time, our body (and brain) get confused. Cue, the grogginess.

We’re basically giving ourselves jet lag, or social jet lag, as scientists call it. “We may have actually tricked ourselves into thinking we have hopped in an airplane and flown to a new destination, making sleep the subsequent night also challenging,” says Robbins.

If you have snatched, shorter sleeps throughout the week, it’s probably not best to switch off your alarm on the weekend and sleep for hours and hours.

“When we cut our sleep short and have to ‘catch up the next night’ the stages of our sleep will be out of sync, causing us to wake up and feel disoriented after sleeping for longer than usual,” says Robbins.

The best sleep is one that is sufficient (7-8 hours ideally) and consistent, which means it follows a similar schedule from night to night – yes, even at the weekend.

“This allows our body to know when it is supposed to be tired and when it is supposed to awaken,” she says. “Our sleep will organise itself very efficiently within this window, slipping in and out of the various stages that allow us to wake up refreshed.”

So if you’re tempted to have a big kip, try to resist. The best option is to keep sleep consistently throughout the week and make up for lost sleep with a short power nap – 20 minutes should do the trick.

“This will pay back some of our sleep ‘debt’,” says Robbins, “without the tax of the groggy sensation after a longer than normal period of sleep.”