On your stomach
Tummy sleepers have long been told that their position of choice isn't great. That's because they have to turn their necks while sleeping in order to, you know, keep breathing. That causes neck strain that, over time, can lead to chronic pain problems. So, if you're usually laying on your stomach, it might be worth it to train yourself to favour another position. The one potential upside to stomach sleeping? Sexier dreams.
On your side
Sleeping on your side isn't as bad for your neck, but you might end up compressing the nerves in your arms and legs, instead. That's especially likely if you're on your side with your arms overhead, possibly wrapping a cosy pillow around your head. That forces you to put extra weight on the lower shoulder.
On your back
If you're someone who has neck or back pain, this is the best sleeping position for you. But it also makes snoring and sleep apnea more likely. And, if you're laying flat on your back, that can make acid reflux symptoms worse, too. So be sure to prop yourself up with multiple pillows if you're prone to heartburn.