I have believed this with humans ever since I watched both parents fight cancer, both at least twice. My father was strong and on his first diagnosis was determined not to let this beat him. In the world of cancer they have a marker which is 5 years clear and you are in a good spot. He was approx 5 months off that mark when we got the news that lung cancer had now appeared and within 6 weeks he had passed. He had made the call he could not fight it anymore and that is how quick it had taken - mind of matter.
Healing is I believe 90% of the mind and the rest is medicine/technology etc. I recently saw an example of this with horses. A client who has an amazing bond with her horse asked me to look at a video of her horse - clearly lame looking like 2 legs diagonally which is not uncommon given their gait. The horse was away from the owner and had a “paddock” accident. I accompanied the owner in order to see if the horse was ok and start treatment asap.
This horse had been away for two weeks and upon arrival I swear he perked up when he saw the float. Oh we were picking him up and bringing him home, the incident that happened was not clear and well he was better at home. I got in and examined him, yes he did have a hoof injury (not my expertise) but feeling around his hind had scrap marks. He was still limping as we placed him in the float.
It was a lengthy trip so with his injuries I would have imagined he would be uncomfortable and swelling to increase. I was dropped off to head my journey home and not long after I arrived home, his owner sent me a video of him walking almost normally. He was home in the surroundings he loved with the herd he loved - his human.
So whilst I can treat your horse or dog they will often need your comfort and love to get over the biggest hurdle which is that they need to heal to be with you, one of the strongest bonds you can have.
Your mind can make you sick but it can also heal you with the ones you love.