For those who care about the consequences
When my horse is showing signs of discomfort, what steps should I take?
  1. The first step is to be sure that there is no physical injury or wound.
  2. Checking the teeth and gums  is important; here is a link that will explain in detail.
  3. A blood sample may be necessary.
  4. Look where you are sitting!  Here is an article on the danger of a badly-fitting saddle.
  5. A check by your osteopath could be advisable. Some thermographic images might help him.
  6. Hoof trimming and/or a blacksmith’s care
Then, if everything is in order and your horse is still showing signs of discomfort, one can consider the emotional component by listening and observing.