Here’s why you feel crap on hot nights.
It’s been dubbed the “heat hangover”: after sleeping through a hot night, you awake to find yourself with all the energy of a sweaty zombie – despite not having anything to drink at all.
Most of us simply put it up with it, because sleeping poorly in summer is as routine as going to the beach or watching the cricket in your undies and pretending you know what’s happening.
But what if you just can’t function without a solid eight hours of shut-eye? Do you simply curse your body for being so fragile that it can’t rest unless it’s swaddled in the finest Egyptian cotton, and get on with it?
Not quite, says deputy chair of the Sleep Health Foundation Professor David Hillman, adding that there’s nothing wrong with you at all – it’s extremely common to feel crappy after sleeping through high overnight temperatures.
“The hot weather in summer – particularly here in Australia – can be really quite disruptive to our sleep,” Hillman tells Coach.
“Ideally, the ideal temperature for a quality night’s sleep is actually the most comfortable – somewhere between 18 and 21 degrees. That could include wearing pyjamas and perhaps a light blanket.”
The reason why this happens, explains Hillman, is all down to physics: the hotter the weather is, the harder our bodies have to work to keep us cool.
“Once the temperature of your bedroom rises above 24 degrees, your body begins to go beyond its thermo-neutral zone – that’s where a completely naked human body is comfortable, and doesn’t have to do anything ‘extra’ to cool itself” explains Hillman.
“Higher than 24 degrees, and your body begins to try and regulate its temperature through evaporative heat loss. You begin to sweat more and your blood circulates closer to the skin to cool you off more efficiently.”
Sleeping in a puddle of your own filth sounds all well and good if you can actually stay asleep – but Hillman says that’s precisely the problem.
“In really high temperatures – like the overnight 30 degrees we just had in Sydney – your brain won’t accept the amount of thermoregulation it has to do, so it wakes you up,” says Hillman.
“And it’s this sleep disruption causes by the heat that causes the symptoms of a bad night’s rest like lethargy and fatigue in the morning.”
So there you have it: your heat hangover is caused by your brain being unable to deal with you being a sweaty mess in bed.
But not all hope is lost – it is possible to keep a cool environment in summer without having to pull your mattress into the nearest bottle shop coolroom.
“If people are struggling to sleep in the heat, some helpful actions can be to make sure you’re sleeping in lightweight cotton instead of nylon, and try to get some air circulation by using a fan or opening a window,” suggests Hillman.
“Remember your body cools itself best with air movement and moisture – that’s evaporative heat loss – so having air circulating in your bedroom and over your sweat helps.”
Other methods to ensure a properly chilly night’s sleep include a cold shower before bed, popping your sheets in the freezer and avoiding any horizontal dancing with your spouse.
“Needless to say, during the heat it’s not a good time for cuddling – give your partner some space if you’re struggling to sleep in hot weather,” adds Hillman.
It may sound like a whole lot of fuss to be preparing your bedroom for sleep like a surgeon prepares his tools for an operation, but Hillman argues that it can carry some profound benefits.
“Interestingly, what I find is people are quite reluctant to prioritise their bedrooms for sleeping,” says Hillman. “If you break it down, we spend a third of our lives sleeping, so it’s actually quite wise to invest in creating an environment that’s as comfortable as possible.
“That may mean purchasing a quality set of bedsheets, a good quality mattress, and looking in to getting air conditioning or a fan to circulate air.”