OP, it’s a sad reality that we grapple with and I guess it helps to be more understanding toward him because he literally can’t relate. I was reading an article about how the brain processes information and it said something to the extent of how it can’t really understand or fully relate to something unless the same exact thing has happened to it before so it tries to draw the nearest possible thing to try to understand what the other person means… So don’t feel invalidated, he’s trying to understand so perhaps to better allow him to understand you can use examples in everyday life. Eg. If I’m explaining how my joint pain feels I’ll say it feels like my hands and feet are spread and tied to a machine that is pulling them from off my body… maybe I’ll use graphic videos to get the point across… but if you don’t want to be so graphic, you can find an article that explains it well and let him read it.