Featured below is an interesting article from Harvard Health Publications on how important sleep posture is to the quality of your rest. Poor sleep posture can cause twisting of the spine putting tension on the muscles that surround it. This in turn reduces circulation, which causes muscle fatigue. The natural reaction of fatigued muscle (to protect itself) is spasm which we feel as stiffness and soreness and restricted range of movement.
"Two sleeping positions are easiest on the neck: on your side or on your back. If you sleep on your back, choose a rounded pillow to support the natural curve of your neck, with a flatter pillow cushioning your head. This can be achieved by tucking a small neck roll into the pillowcase of a flatter, softer pillow, or by using a special pillow that has a built-in neck support with an indentation for the head to rest in. Here are some additional tips for side- and back-sleepers:
Try using a feather pillow, which easily conforms to the shape of the neck. Feather pillows will collapse over time, however, and should be replaced every year or so.
Another option is a traditionally shaped pillow with “memory foam” that conforms to the contour of your head and neck. Some cervical pillows are also made with memory foam. Manufacturers of memory-foam pillows claim they help foster proper spinal alignment.
Avoid using too high or stiff a pillow, which keeps the neck flexed overnight and can result in morning pain and stiffness.
If you sleep on your side, keep your spine straight by using a pillow that is higher under your neck than your head.
When you are riding in a plane, train, or car, or even just reclining to watch TV, a horseshoe-shaped pillow can support your neck and prevent your head from dropping to one side if you doze. If the pillow is too large behind the neck, however, it will force your head forward.
Sleeping on your stomach is tough on your spine, because the back is arched and your neck turned to the side. Preferred sleeping positions are often set early in life and can be tough to change, not to mention that we don’t often wake up in the same position in which we fell asleep. Still, it’s worth trying to start the night sleeping on your back or side in a well-supported, healthy position."
Read more: http://www.health.harvard.edu/healthbeat/HB_web/say-good-night-to-neck-pain.htm