I had lost the arm as a child due to some sort of animal attack, but the fact that I didn't escape the animal before it severely chewed my arm such that it required amputation at the shoulder, was because in the dream I also had some sort of disorder that made me experience occasional "attacks" wherein I lost motor control and sensation in my limbs.

In any case, I was really into guns in this dream, I was in a shooting club and everything, and more specifically I was fascinated by the history of how firearms have been adapted for those with upper limb amputations and prostheses, especially the type of prosthesis that I had. I had in general made the arm a part of my identity, like I wasn't ashamed of it, I'd make jokes about it, I'd wish that the arm would work "more like in the movies" but I still managed to navigate my daily life just fine.

I guess if anything, I woke up feeling kind of freaked out by how my brain had managed to come up with such a radically different path for my life, and made me accept this path so unquestioningly, as if I had really been on it the whole time. It was kinda like Zhuangzi's famous butterfly dream in a sense, and made me wonder how much people should really stake on something so fragile and malleable as identity.