Isn't it wonderful to wake up feeling well rested and pain-free?  Sleeping in the right position has a lot to do with that. The advice from the Mayo Clinic is to use pillows or rolled up towels in crucial spots to keep the body aligned.

If you sleep on your side, it is recommended to:
Place a pillow between your knees and possibly a small towel rolled under your waist if it is more comfortable.  This will relieve pressure on lumbar joints and your spine will be more in alignment.

If you sleep on your back, it is recommended to:
Place a pillow under your knees (this feels so good) and a small pillow or rolled towel under your back.  This causes your knees to be slightly bent so your spine will stay naturally curved.

If you sleep on your stomach, it is recommended to:
Place a pillow under your hips and under your ankles. Placing the pillows in those areas will help those who have bulging disk problems in the lumbar region of the spine.  Consider not using a pillow under the head when laying on the stomach to minimize stress on your spine.

Using pillows as suggested, assist in taking the pressure off your spine and allows the disks to recuperate overnight.  It is also suggested to use only one pillow under the head so that there is little chance of causing misalignment and pain in the neck area.