If you haven't shaken off that heatwave tiredness yet, you're not alone. Abi Jackson asks experts what it's all about.

The sweltering peak of the heatwave might be over - thank goodness - but many of us are still feeling sluggish and exhausted.

So, now the mercury's dropped back to a more reasonable summertime range, why haven't our energy levels snapped back too?

You might have a 'sleep debt'

"People will have incurred a sleep debt - perhaps above and beyond their normal sleep debt," suggests Dr Guy Meadows from Sleep School (sleepschool.org).

"Nearly three quarters of the population walk around with a sleep debt anyway - as in they're not achieving their biological sleep need, which is roughly seven to eight hours a night for most of us. So we can all already do with sleeping a bit more, but during the heatwave, we were struggling to sleep even more."

Meadows says that while we're awake, a brain chemical called adenosine builds up in our systems, helping create 'sleep drive' - so we're ready for sleep come bedtime. "The more adenosine you have in your system, the more sleepy you feel. If you then get your eight hours of sleep, your adenosine is metabolised from the brain, and you wake up feeling refreshed," he explains. If we don't get enough sleep to metabolise these chemicals, we wake up feeling groggy - the sleep debt effect.

"The great thing is you can repay a sleep debt," says Meadows. "But what I would definitely not recommend is people go and have a big, long lie-in, because what that does is cause 'social jetlag'. Put simply, big lie-ins 'upset' our circadian rhythm or natural 'body clock', which also leads to ongoing grogginess."

So what's the best thing to do? "Repay your debt in small chunks over a period of time," Meadows advises. If you really want a lie-in, keep it to "no more than one hour maximum". And "maybe have a little power nap after lunch, 15 or 20 minutes, that can help. And going to bed 30 minutes earlier. Little catch-up opportunities over the next week will help restore the debt."

Heatwaves are hard work!

Another thing? Getting through the heatwave was hard work for our bodies - it took up more energy than usual, plus there's a good chance we became a bit dehydrated, and didn't move and exercise like we usually might. It might take a minute to shake off that slow, sluggish feeling.

"As a GP, I often have people asking me why they feel more tired in hot weather," says GP and mental health coach, Dr Hana Patel (drhanapatel.com).

"We sweat more in hot weather, as this process allows our skin to cool when the sweat evaporates. Another of our body's natural physiological responses is to allow more blood to flow to the surface of the skin, to release heat. Both of these actions take up a lot of energy, increasing our heart rate and burning calories, making us feel extremely tired and sleepy."

And let's not forget: while it might not be so overwhelmingly hot right now, it's still warm, so we're still adjusting to the heat. Fingers crossed temperatures remain in more moderate zones - so we can catch up on those precious ZZZs and get our energy back.