When I was 12, I was in an accident that shattered part of my upper jaw and my nose. It also busted apart the skin between my upper lip and the bottom of my nose. I lost teeth that hadn't even come in yet, and my jaw still has a dip in it that I cover with false teeth. Some of the tissue of my face disconnected from my skull and had to be sewn back in place.
I still have a small scar and a slightly crooked nose, despite reconstructive surgery.
I didn't hear it because the impact was sudden and knocked me unconcious.
When I woke up, I was in shock. It took me several seconds to remember that breathing was necessary. My thoughts were incredibly detached and logical. I just laid there, staring up at my horse for a moment. Then I Oh, yeah, I need to breathe. Next thought: I better spit out whatever's blocking my throat if I want to breathe. I did so, and saw blood, tissue and teeth. Damn, that sucks. Then I thought better catch the horse and put her away. I caught my horse, got on her, took her back to the barn and took off all her tack, then started walking home. I was almost to the door and suddenly, I felt strange, and scared...it was the first time that I felt fear, and I still didn't feel pain.
I tried to tell my mom that I didn't want to see a mirror - I knew that seeing the injury might freak me out or make me feel the pain more - but my face was so blasted that my mom couldn't understand what I was saying.
We didn't have a car with us, so a neighbor arrived to take us to the hospital, but he had his granddaughter with him. She stared at me in mute horror. At this point, amnesia set in. I told the little girl that I was OK, and it didn't hurt, then turned to my mother and asked "What happened?" Before she could respond, I told the little girl that I was OK, then asked again. I did this all the way to the hospital without realizing that I was repeating myself. It was surprising how little blood there was at this point. Almost none.
Anyway, I'm including all this because what I was experiencing is common to extreme bodily trauma...it's shock. The injured character, if they are injured severely enough, may experience shock...in which case, their actions and thoughts may not be what would normally be expected, and they may suffer amnesia. In my case, the amnesia had a definite, sudden onset and I forgot the entire traumatic event, all the way up to the present moment, every 20 seconds or so. After about 30 minutes, I remembered the details of what happened just prior to the accident and arriving at my house after the accident. It took me years to remember the whole event.
PS - That was a darn good horse. We were attacked by dogs, and she reared unexpectedly. The back of her neck shattered my face and knocked me out. When I woke up, she had fought off all the dogs and was standing over me protectively. When I reached for her, my hands were bloody, and she shied away but let me catch her, and when I slung myself over her saddle, she carried me gently home. She even followed me back to my house on the other side of the fence, watching me like a mother hen. So yeah, I still love horses.