It sounds to me like you have your mind but not necessarily your brain. The philosophical musing is you but the not being able to switch it off or turn it down sounds very much like a current brain chemistry problem. I used to have something similar when I was a kid. I would get fevers and my brain would obsess about numbers. I would count, add, subtract, shuffle them, picture them in my head until I couldn’t stay awake and then dream numbers. Lucky for me I naturally grew out of it but I sympathise about how noisy and distracting it can be unable to to tune out. These days there are much more options for stabilising brains. There are the chemical options your GP might offer but learning some sort of meditation techniques where you can shift the focus onto breathing or some other physical connection would be good skills to have.