"Physiologists divide nerve-fibers, which form the nerves, into two classes, afferent and efferent. Impressions are made on the peripheral afferent fiber-endings; these create sensations that are transmitted to the center of the nervous system. Efferent nerve-fibers carry impulses out from the center to their endings. Most of these go to muscles and are therefore called motor impulses; some are secretory and enter glands; a portion are inhibitory, their function being to restrain secretion. Thus, nerves carry impulses outward and sensations inward. The activity of these nerves, or rather their fibers, may become excited or allayed by impingement, the result being a modification of functionality – too much or not enough action – which is disease."
Research suggests that not just sleep position, but sleep itself, can play a role in musculoskeletal pain, including neck and shoulder pain. In one study, researchers compared musculoskeletal pain in 4,140 healthy men and women with and without sleeping problems. Sleeping problems included difficulty falling asleep, trouble staying asleep, waking early in the mornings, and non-restorative sleep. They found that people who reported moderate to severe problems in at least three of these four categories were significantly more likely to develop chronic musculoskeletal pain after one year than those who reported little or no problem with sleep. One possible explanation is that sleep disturbances disrupt the muscle relaxation and healing that normally occur during sleep. Additionally, it is well established that pain can disrupt sleep, contributing to a vicious cycle of pain disrupting sleep, and sleep problems contributing to pain.
Chiropractors use hands-on spinal manipulation and other alternative treatments, the theory being that proper alignment of the body's musculoskeletal structure, particularly the spine, will enable the body to heal itself without surgery or medication. Manipulation is used to restore mobility to joints restricted by tissue injury caused by a traumatic event, such as falling, or repetitive stress, such as sitting without proper back support.