Arousal is usually the term used to describe such a physiological reaction.
From the en.wikipedia.org
When we get too hungry, the normal physiological reaction is to overeat.
From the blogs.psychcentral.com
It's as you say a physiological reaction, sometimes occuring without any obvious stimuli.
From the guardian.co.uk
The body's physiological reaction to time change may be complex.
From the sciencedaily.com
These served as a behavioral measure of physiological reaction potentially related to reward anticipation.
From the sciencedaily.com
Emotional memories are consciously available, but elicit a powerful, unconscious physiological reaction.
From the en.wikipedia.org
By contrast, patients with OFC dysfunction never develop this physiological reaction to impending punishment.
From the en.wikipedia.org
Housed in this physiological reaction, the needs of the person intersect, instantly, with the needs of the horse.
From the blogs.psychcentral.com
Maybe it is that the horse needs nurturance, and the person needs to feel valued, and in that instant, there is a physiological reaction that is shared.