I'm getting the impression than you think you only exist in your head, whereas I do not, and this is a material disagreement on the self.

The measurable difference is that my conception of the self includes the embodied self and the social self. I am, in part, my body. I am, in part, my place in society. I am, in part, my relationships.

There is a dialectical relationship between the internal world inside our heads and the real world outside of it. Narrowly focusing on the brain misses this nuance.