Autogynephilia is a real phenomenon whether you can relate to such a thing or not. There is no such thing as a feminine brain being inside a male body, vice versa. If there was there would be an obvious genetic component to the issue, and besides, the idea of a valid gender (separate from a person's biology) comes from the Talmud/ Zohar. The very simplified version is this: there is a general escalation that comes with porn addiction, and that can also lead them to become sexually intrigued about the female perspective, paying attention to their orgasms and such, and start fantasising about being female, and it gets worse from there. All manner of weird paraphillia can be generated from such an unhealthy lifestyle and interest, but it's this one that gets a lot of external validation and media exposure.