A vertical position is the normal posture of the human body.
One function of the spine is to hold the head straight.
When the head misaligns (due to falls and traumas) the spine shifts to find a new center of gravity, which then changes the individual’s normal posture.
This causes misalignment of the cervical spine, shoulders, torso, and pelvis. It also causes what is known as leg length inequality.
That misalignment and its effects on the nervous system is called "vertebral subluxation" by the chiropractic profession.
Another function of the spine is to protect the nervous system that runs through the spinal and neural canals. When the spine misaligns it can irritate the spinal cord as well as the nerves that branch off the cord. This may cause health problems.