Tension is a state of being stretched tight giving people an experience of their body as pulled tense and tight. The natural state of the body musculature is viscoelastic which means when under tension muscles can deform altering posture as well as lead to compensation(s).
As muscles continually under tension deform, they change the posture and uprightness of the spine causing the spinal joints to stub, overload and dehydrate. Joint loading under muscular imbalance becomes wear and tear.
The spine is not in the centre of the skull, it is about 2/3rds toward the back of the head, causing the centre of weight to be forward. Thus, the head will naturally fall forward, placing more tension onto the neck and shoulder muscles of the back. This tension is required to be balanced with the jaw to give an upright facing forward posture.
There are several muscles that can go wrong due to excess tension around the neck and shoulders, each one able to give neck, shoulder, face and head pains. Including in and around the eyes and the top of the back in between the shoulder blades. Once a muscle is strained through excessive tension then posture will alter due to the viscoelastic nature of the body.
Chronic neck and shoulder discomfort will likely lead to more compensation strategies that place excessive tension somewhere else in the body eventually affecting more and more of the spine, jaw and posture.