Balancing the nervous system is essential, but it will take more than this.
This position is known as "neutral back" in physical therapy. More to the point are ways to release the psoas muscle that can bring about deep relaxation of muscle and realign the core all the way up to the neck. One is called "corrective rest" and there different ways to do it. You will walk differently.
Even more important can be an underdeveloped palate that that imposes sympathetic overdive You have to address the whole container of the nervous system from the cranium to the sacrum. There are ways to expand with tongue, fingers, and orthdontic appliances.
All these should free the breath when they work. I will post my article on dental subluxation later, and my website describes a the Brain Body Balance method that describes how i put these things together.
Most chiropractors, like other health specialists, are missing a big part of the picture. They miss how the teeth and narrowness of the upper palate determine posture, the nervous system and brain.
The basic idea of chiropractic is that vertebrae that are not aligned pinch nerves to create pain and restrict flow of impulses to organs and organ activity. The worst case is when the brain is constrained, as the command center of the nervous system. When the upper palate is underdeveloped from childhood (as seen in crowded teeth) the cranial bone next to that, the sphenoid, is constrained and that crowds the other cranial bones and can affect brain functioning. Cranial bones are actually separated by small sutures, including the bones of the upper mouth.
When the bones are crowded it stresses the brain to create a permanent stress response, low level and imperceptible, known as autonomic nervous system disregulation or sympathetic overdrive.This weakens ability to rest, heal, and regenerate and thus can be one root cause of many diseases and symptoms like "adrenal fatigue," chronic fatigue, insomnia, sleep apnea, and just about anything. This is systemic problem much bigger than any particular nerve in the back or neck,
Posture is affected because a narrow palate creates a narrow airway which requires a forward head posture to breath. People with this constraint have trouble talking when they bring their head back over their shoulders. This curve in the neck sets up excessive curves all the way down the spine, often with forward hip posture and a sunken chest familiar to all since this has become a postural epidemic.