There are two approved methods of sleeping recommended by the American Chiropractic Association: sleeping on your side and sleeping on your back. Sleeping on your stomach is not only the least desirable position to sleep in, but it could damage your spine and nervous system. Sleeping on your back is the preferred position for good sleeping posture, but sleeping on your side is acceptable if it doesn't cause back pain. However you sleep, the ACA recommends you sleep on a firm mattress unless it feels better for your back to sleep on a softer mattress.
Sleeping on Your Back Correctly
Roll up a sheet or towel. Tie the towel around your waist to provide support for your lumbar spine. A lumbar support allows your spine to retain its neutral and proper alignment.
Lie on your back on a comfortable and supportive mattress. Place a pillow or small bolster under your knees. Bend the knees slightly. Relax and let your thighs and feet turn out.
Place a buckwheat or sobakawa roll under your neck in lieu of a pillow, as recommended by chiropractor Chip Abbadessa of Kaneohe Family Chiropractic in the Midweek.com article, "Sleep Posture." Use a roll that is the same thickness as your neck.
Sleeping on Your Side Correctly
Lie on either your right or left side. Rest your head on a standard pillow that is the correct thickness so your face points straight ahead. Avoid a thicker pillow that will cause your neck to rotate up or a thinner pillow that would turn your face toward the bed.
Bend your knees slightly and place a pillow between your knees to keep your pelvis stable. Do not twist your pelvis or your spine will not be in the correct alignment. Keep your knees away from your chest and avoid sleeping in the fetal position, warns The Cleveland Clinic in its "Posture for a Healthy Back" article.
Switch sides occasionally so that you do not always sleep on one side during your lifetime. Sleeping on one side causes your chest and spine to eventually shift to one side, warns Abbadessa.