Eight hours of sleep (a third of your day) is what most health-care professionals suggest for their patients. Does it matter what position you sleep in, as long as you sleep? Definitely! After a night of improper sleep posture, spinal bones can become misaligned (subluxated).
Some people sleep on their stomachs, while others sleep on their side or back. The optimum sleep position is back-to-mattress, with the head and neck cradled in a cervical pillow. The goal is to keep the spine as close to its normal alignment as possible, and sleeping on your back keeps your hips aligned evenly. When the curves are over-exaggerated or reversed, you risk structural shifts in your spine (vertebral subluxations) and related disorders such as arthritis.
Sleeping on your stomach is the worst position for your spine because it torques the spine of the neck, reversing the normal curve, and forces rotation. It can also cause arm pain because it’s not unusual for a stomach sleeper to extend one arm over or under a pillow. The pain, not surprisingly, is connected to the over-stretching of the arm throughout the night. This prolonged position restricts the blood supply to the rotator cuff, which is a contributing factor to shoulder impingement.
Curiously though, sleeping on your stomach has been shown to alleviate sleep apnea. So what to do? Best thing is to get onto your side or back. If you are a chronic stomach sleeper (I was for years), wedge a body pillow under your chest and work to be on an angle versus directly on your stomach.