First my condolence for your injuries and attack. I hope you are recovered and well.
I went through a similar attack to the one GZ describes and I did not bleed all over the place. My attacker focused on my head and face, surprising me from behind, throwing a punch as I turned, sending me to my knees and repeatedly punching me in the face and once I was laid out, slamming the back of my head into the floor again and again. I did not bleed profusely. I do not recall injuries or bruising to anywhere other than my head and face. The painful lumps on my scalp were not visible as I had long hair. The bruising and swelling on my face was severe, the bruising lasted for what seemed like forever and my left eye socket was sensitive for years. I was able to walk and, although I was an emotional wreck, I became very quiet and withdrawn which may have been perceived as "calm as a cucumber" but I was nothing near calm on the inside.
IMO, I would like to know what GZ looked like the morning after as I believe that's when the bruising would really start to show. We've heard some statements from neighbors that he was wearing bandages and his nose appeared swollen, but I wonder how good a look they got of him. IOW, I don't feel that the statements, as they stand, tell us a whole lot.
I've found GZ's account to be believable and I think his demeanor can be attributed to shock. However, I doubt he was beaten as badly as you or I. Still, I understand the overwhelming fear that your skull won't be able to withstand another blow which IMO makes a "reasonable" self defense claim. I put the word reasonable in scare quotes because I don't personally find it reasonable but I can understand why other people, and the law, would.
ETA: I feel you on the personal experience. Whether or not GZ is to be believed, this case has really brought back some bad memories that I've had to revisit and rethink. And it's added a level of emotional connection I can't shake. Totally OT but I just wanted to say I'm with you on that!
JMO, OMO, and :moo: