As a side sleeper, you need to accommodate the gap between your head and shoulder. Your neck should remain at a 90 degree angle from the line of your shoulder (as depicted above). If you typically need to put your arm under your head or use two pillows, its time to get a new pillow.
To help prevent stiffness in the neck muscles, side sleepers should keep their head and neck aligned with the rest of their body.
Use a small pillow underneath the head and neck (not shoulders) to keep everything in alignment. Even better, a small cylindrical pillow in the crook of your neck supports your neck and keeps your head neutral on the mattress. Do note, though, that this sleeping position can cause some people to snore.
Proper alignment of the neck should resemble a backward “C” – similar to the “C” shape of a banana. This neck curve allows for correct motion, including flexion and extension with health range of motion. If the cervical curve is lost, the neck can resemble a straight line, with bones stacked vertically.
Check your Neck – Cervical spine misalignment can inhibit full range of motion in your neck. If you can't seem to twist your neck fully to your left or right, or pain develops when you turn in one direction, odds are you're dealing with an alignment issue.
Your cervical spine is made up of the first seven vertebrae in your spine that span the base of your skull to your thoracic spine (the area between your neck and abdomen). A healthy cervical spine is shaped like a wide-looking “C” with its curve facing toward the front .
Neutral Head and Neck Position
Your chin should be level and, generally, the gaze of your eyes should be forward. There should be no tension in the muscles around your neck, and your neck should hold its neutral position with a gentle anterior curve, called a lordosis.
Pull your knees up slightly toward your chest. The pillow for your head should keep your spine straight. A rolled towel or small pillow under your waist may also help support your spine. Insert pillows into gaps between your body and the mattress.
Sleeping flat on your back will help keep your spine aligned and it allows your body to follow its natural curve so you aren't putting any unnecessary pressure on your back. To help keep this curve in the most natural position possible, place a small pillow underneath your neck and one under your knees.
Tucking the pillow under the shoulders will position the head further up on the pillow, so the neck is not flexed (bent forward). This position may feel as though the head is more extended slightly, and may be more comfortable for those with muscle pain in the neck.
Sleeping on your back may be one of the best positions for improving your sleeping posture. It promotes better alignment and reduces the pressure on your arms and legs. People with neck or back pain, especially in the lower back, find it to be the most comfortable.