In general, people experiencing constant pain, physical or emotional, will do anything, rational or not, to assuage that pain. It can be doing what you've witnessed, it abusing painkillers etc

Yes, I believe we can communicate with our subconscious, this is what I think we call "instinct" or "gut feeling", which is extremely important part of who we are, and how we navigate the world. However, I don't know if the arm test is really a good and reliable way to access our subconscious. 😅

On a related note, I watched a video (🇫🇷) yesterday, an interview of a doctor who wrote a phd thesis on miraculous healings. He interviewed 12 subjects who experienced spontaneous healing or remission from stage 4 cancer, after modern medicine couldn't do anything for them. His conclusions were fascinating!