I think I can relate a little. The hypothetical of losing weight has always been in the forefront of my thoughts. "This would be easy if I were thin. I could do that if I weren't so fat. I might have friends if I wasn't so shy because of my size." But it was always detached from who I actually am. An imaginary thin person who was totally separate from myself.
I've identified myself as 'the fat one' so completely and for so long (almost since before I can remember anything else) that the idea of ME, not some figment in my mind, actually being a normal size is mind boggling and a little scary too. I don't know how to relate to the world as someone who is not fat. I don't know how to relate to other people without the self-consciousness about my size. I'm afraid that I will reach goal and still not be good enough, but the safety of knowing I could just lose weight will be gone.
It's something that is getting stronger as I get closer to goal and realize I'm really going to get there this time. I try to remind myself that I am still me, just as much me as I was at 230 lbs. But people always change and evolve. I know I am an incredibly different person than I was four years ago. But that doesn't mean I am any more or less myself. But I think it's because weight loss is such an apparent full physical and mental change it is harder to deal with emotionally because other personality changes are much more subtle and happen naturally, instead of something we force to change ourselves.
Shifting my goals to fitness more, instead of just getting smaller, has helped. Instead of thinking about what I will BE at goal I think about what I will DO. Such as being able to hike a difficult trail longer and quicker, being able to go out and ride bikes all day in the summer, etc.