Sleeping positions/posture can affect the pressure on your body and quality of rest. And if you are already suffering from pain, chronic or acute, poor sleeping posture may lead to not enough rest and possibly make the pain worse. Although everyone is different, here are some general guidelines.
Sleeping face up allows the shoulders to relax the most. However it increases the pressure on the lower back and can irritate lower back problems. Also, sleeping face up reduces acid reflux but it does increase chance of snoring.
Side-sleeping is also common. Sleep on the right has less pressure on organs and sleep on the left relieves acid reflux and increases circulation to foetus while pregnant. It does put pressure in the shoulders and ribs which can lead shoulder and arm stiffness and stressed breathing.
Sleeping on your stomach helps with snoring. However, such position puts pressure on joints and muscles, which can irritate nerves and lead to pain, numbness, and tingling. Sleeping on stomach also means over stretching your neck muscles and ligaments because your head is turned very far for long hours. The benefits are far less than harm; should avoid sleeping face down.
Check with your doctors on what is best for you if you suffer from chronic pain or discomfort.