Side sleeping is the most common sleep position, and experts agree that it’s typically also the healthiest. Leeds explains that sleeping on one’s side provides relief from back pain and may reduce one’s risk of breathing problems like sleep apnea, while Park notes that it tends to promote good circulation. However, the sleeping position also comes with some potential downsides.

The key to restful, restorative sleep is to keep your spine, neck, and shoulders all in good alignment. But picture the shape of someone sleeping on their side: The widest parts of their body, their shoulders and hips, will naturally want to sink deeper into a mattress.

If your mattress is super firm and doesn’t have enough give, you might wake up with shoulders and hip that feel sore or stiff in the morning. If it’s really soft, your shoulders and hips may sink too far your mattress and throw off that ever-important alignment, which can irritate your joints and ligaments and contribute to low back pain.

“If you have too soft of a mattress, regardless of your sleep position, your body kind of gets absorbed into that,” Koth says. “It might feel good, but your body has to do absolutely no work. Without a little bit of muscle contraction to stabilize you, you actually lose some of the support that your body needs.”

From head to toe, experts say side sleepers should aim for the following alignment when sleeping: