If you live in any location that was hit by a heat wave last year, you probably spent the night tossing and turning, trying out different sleeping positions in an attempt to get comfortable.
But what does the evidence say - which sleeping positions are actually the best?
A study of everyone from seafarers on container ships to welders in Nigeria could help us find out, though given how important sleep is to us, surprisingly little large-scale research has been conducted.
First you have to find a way to determine what positions people sleep in anyway.
You can, of course, ask them, but we only remember how we lay while trying to fall asleep and the position in which we wake up.
To learn more, researchers have tried a variety of techniques, including recording people while they sleep or with wearable technology that monitors their movements.
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In Hong Kong, researchers are developing what they call a "Blanket-Friendly Sleep Position Classification System" that uses infrared depth cameras.
They can detect sleeping positions even through a thick blanket.
Scientists in Denmark used sensors that detect minute movements attached to volunteers' thighs, upper backs and upper arms, placed before they fell asleep, to determine their preferred sleeping position.
They found that during their time in bed, people spend half of their time on their sides, about 38 percent of their time on their backs, and seven percent of their time on their stomachs.
The older people were, the more time they spent on their hips.
We only develop this tendency to sleep on our sides when we grow up, because children over the age of three, on average, spend an equal amount of time sleeping on their sides, backs, and stomachs.
Babies, during this time, generally sleep on their backs because they are left in their cribs that way for safety reasons.
So, sleeping on your side is the most common sleeping position and we can trust the wisdom of the majority that they will choose the position in which they sleep best, but what does the data say?
A very small observational study in which people were allowed to sleep as they preferred, found that those who slept on their right side slept slightly better than those on their left, followed by those who slept on their backs.
If you find that it's easiest for you to sleep on your side, then it's probably best for anyone else trying to fall asleep near you.
On one occasion when I was touring a submarine for a radio show I was recording, the submariners showed me the sleeping quarters, where the beds were stacked so close to each other that it was difficult to turn around.
This meant that they were in the habit of sleeping on their backs, so they told me that it was always a race to see who would fall asleep first, as the entire cabin was full of snoring men.
Another small study looked at seafarers working on merchant container ships and found that respiratory disorders such as snoring were more common when seafarers slept on their backs.
Some snoring is caused by severe obstructive sleep apnea, in which breathing stops and starts again while the person sleeps.
It has been shown that it is more common in people who constantly sleep on their backs.
By comparison, lying on your side helps clear your upper airway by preventing the uvula (the fleshy part that hangs deep in your throat) and tongue from blocking your throat, leading to less snoring.
And indeed, in some cases, switching from sleeping mostly on your back to sleeping mostly on your side has been shown to completely resolve the apnea problem.
Sleeping on your side could have other benefits as well.
For example, a study of the sleeping habits of welders on container ships in Nigeria found that those who sleep on their backs are more likely to suffer from pain in that part of the body than those who sleep on their sides.
But that doesn't mean side sleeping will work for everyone or that it's a panacea for all aches and pains.
It depends on your personal complaint and the exact position you take during sleep.
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Researchers in Western Australia monitored volunteers' bedrooms for 12 hours a night using automatic cameras.
They found that those who claimed to regularly wake up with a stiff neck spent more time in what the researchers called "provocative side sleeping positions."
This term might conjure up all sorts of possibilities in your head, but in this context it means sleeping on your side in a crooked position: for example, with your upper thigh over the other, which twists your spine.
By comparison, people who slept in a more upright position said they had less neck pain.
What the mechanism of this study could not determine is whether sleeping in a "provocative" position causes neck pain or whether people took that position because it was the only comfortable one in which they did not feel neck pain.
What if people tried a new sleeping position and you tracked them to see if it made a difference to their pain?
In a study of older people participating in a fitness program in Portugal, people with back pain were told to sleep on their sides, and those with neck pain were told to sleep on their backs.
Four weeks later, 90 percent of the participants reported that their pain had decreased.
This looks like an impressive result, but there is one caveat.
Only 20 people participated in the study, which is a very small sample, so it is not possible to conclude whether this simple change in sleeping position could have such a positive effect on anyone suffering from back or neck pain.
As usual when it comes to scientific research, additional studies need to be done.
As for another medical condition, it's not just a matter of whether you lie on your back or side, but which side.
In acid reflux, gastric juices rise up from the stomach, causing a severe burning sensation in the chest.
Doctors sometimes advise people to try sleeping on elevated pillows in an attempt to alleviate this very unpleasant type of pain.
If this discomfort is repeated regularly, then it is also known as gastroesophageal reflux disease, which can have serious consequences.
Why this happens is not entirely clear, but one possible explanation is that sleeping on the left side keeps the junction between the stomach and esophagus above the level of stomach acid.
Sleeping on the right side relaxes the lower esophageal sphincter, allowing acid to escape.
Whatever the answer, if you suffer from heartburn, it might be worth your while to try sleeping more on your left side in the future.
So far I've focused on sleeping on my side or back because that's what most people do.
But what about those people, a very small minority, who sleep on their stomachs?
For starters, one study suggests it's not a good idea if you suffer from a painful jaw, which probably won't surprise you too much.
But what about wrinkles?
If you lie with your face stuffed into a pillow, surely that deepens your wrinkles?
Writing for a magazine Aesthetics of the heart, a group of plastic surgeons suggested, rather poetically, that the best way to preserve facial skin is to treat it like "seaweed that waves while tied to a stalk."
So the idea is to apply as little pressure as possible to your face while you sleep, and that excludes sleeping face down.
And if preserving your skin is more important to you than better sleep or fighting the pain and suffering of reflux, then sleeping on your side is not the most ideal solution either.
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So what can we conclude from all this?
First, if there are no other factors affecting you, sleeping on your side seems to have several advantages, but your exact position can affect neck and back pain, and the side you sleep on can increase or decrease your reflux.
Snoring gets worse if you sleep on your back, but we're all different, so it may still be the way you sleep best.
It pays to try new sleeping positions and keep a journal if you're not sleeping well in your current position.
But remember that you shouldn't be obsessive about different positions, because you might stay awake because you worry too much.
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