Startle response definitely relates to the pull of our head and the tension in the neck. The point I want to make is that this pattern of the muscle contraction in the neck and pulling the head back and down is the same as the pattern which a person hold their body (including the head) too firmly.
Now, we maybe learn the pattern, because we have felt fear or startled frequently enough. At the same time, we maybe learn the pattern, because we have held our body too firmly frequently enough.
In either cases of the causes (the former and the latter), we can’t change our past. All we can do is to change the current condition for our current and future life. Something we know is that we probably can’t stop our startle response when we are startled.
Now, both causes are possible. Then, given the latter cause (supporting habit origin) come from a person’s way of supporting the body, there will be possibility for a person who has the pattern to correct their pattern to adequate one, through changing their way of supporting their body. This is also applicable for the person whose cause is the former(fear origin), because the pattern is the same. So, we have a chance to change our habit through changing the way of supporting the body.
Therefore, I think that the way of supporting the body is the bottle neck of this problem. We should look into the way of supporting the body.
While people in the Alexander Technique have looked into the relationship of the head and neck (and back), it seems to me that we haven’t looked into the way of supporting the body and its mechanism so much. There is advantageousness in the way of supporting the body. There is a field for us to look into more.
My idea is a hypothesis from this point of view.