Could be, that this will be his first reaction. But it doesn't getting him immediately calmer thereby? At most it's getting him sidetracked for a moment, I mean.
But body and brain interact. For example, assuming a posture that is typically associated with power (upright, open) for just a few minutes changes hormone levels, increasing testosterone and decreasing cortisol (which is associated with stress). Similarly, relaxation is used as an exercise in psychotherapy and for some anxiety disorders it's even as effective as exposition - and that's also "just" an exercise for the body, but it has effects on the brain and in that way on the emotional experience. I don't know any investigations on changes of hormones and neurotransmitters following head lowering in horses
, but it would not surprise me if these effects were present.
For a few seconds may it works...
But what, if the horse nevertheless constantly peers into distance because there seems to be any wild monsters?
How is he supposed to do that with his head on the ground?
Because that's another beneficial effect of this exercise - with a head that low, the horse cannot possibly get into staring and freezing mode.
Concerning the old posts about head lowering, I realized that there were many of them but they all just said that people were doing it and it worked, but to know that I guess you needn't read all the posts first. So instead, here is a thread that is especially for you and Pan: Treats in anxious situations
. It discusses how people deal with their horse turning into a statue because he sees something scary at the horizon.