You can do this simple test to find out if you have forward head posture. Stand with your heels and shoulder blades touching a wall or door and relax. Is your head touching the wall without you having to pull it back? If your head is off the wall at all, you have forward head posture.
The stomach and liver are attached to the diaphragm, and the suspensory ligament of the diaphragm is the pericardium, especially of the right side, which finally attached to the anterior part of the lower cervical spine. Because of this anatomic make-up it is possible by simply correcting the position of the head, to raise the diaphragm, stomach, and liver one inch or more. If the diaphragm is lowered as a result of the habitually forward position of the head, the movement of the diaphragm in respiration must be less than normal. The effect of this upon the breathing, as well as upon the circulation, especially in the large abdominal veins, to say nothing of the function of the other organs, must be apparent.