Overall, no one knows the full answer. But as an autistic person I do understand the body- brain issue. Many austic people don't feel their bodies in space. I myself feel extreme discomfort if my arms are dangling by my sides. It's hard to explain, but often time my arms feel alien to me eviden i look at them because my brain isn't registering that they're mine. A similar phenomenon is experienced by schizophrenics, they're able to tickle themselves because their brain doesn't register that it's them that's touching themself.

A lot of what trans people say about their experiences sound word for word what austic and schizophrenic people say about how they perceive themselves.