Horrible euthanasia experience

Why was my pets euthanasia a nightmare?

I brought my cat Jack in for euthanasia and the doctor and assistant gave him a needle shot of sedative – in his hind muscle… A muscle shot is very painful! Jack yelped, hissed and jumped up, but then he just sat back down facing me. The vet left me alone with him for a few minute for the sedative to take effect. Jack got drowsy and lowered his head to the table, but never passed out. When the vet came back in, my kitty raised his head to look at him. He said he would need another shot of sedative. I thought it would be no worse than the first, maybe less as he was already under somewhat from the first shot. The assistant had not come back in, so the vet asked me to help hold Jack. I wrapped the towel around his front and feet/ claws and the vet proceeded to give him the second shot. This is where it got nightmarish. Jack yeowed loudly and shot straight at me (my stomach) but was still in the towel and I didn’t know what to do but hold on. He struggled and screamed again and came up off the table and hit the floor half-way across the room. One of his hind legs wasn’t working right, so when he first tried to run he could only go in circles. I wonder if it was just the shot in the muscle or if the needle broke off in him (the vet didn’t say) or maybe he hurt his leg on landing since he was disoriented. Then he started running/skidding and sliding around the room - he ran into and under everything. His front and back weren’t coordinating (besides his back leg not working) so his body kept twisting around and rolling on his back where his vulnerable belly was exposed. Its a terrible thing for a cat to exposed his under belly to a stranger (the vet), but he had no control. He just kept skidding violently around the room running under and into everything over and over. I lost count how many times he went around the room – he wouldn’t stop moving and it went on so much longer than I would have thought. I also fear he associated the traumatic event with me as he was facing me while I helped hold him down. When he went wild, I couldn’t get near him again until the sedative knocked him out. He wouldn’t let me touch him (hissing and crying out violently if I approached him). At one point when he again rolled on his back, he defecated. He’s always been a “nervous pooper” but this was beyond nerves. The vet said he was fighting it hard (the sedative), and might be better if he (the vet) left the room. He turned down the lights and when he left, Jack calmed down somewhat on the other side of the room and looked at me for a moment. He eventually succumbed to the sedative and I held him and pet him in the dark for a few minutes (I don’t know how conscious he was, but he made a couple of small sounds deep inside his body). I had wanted to look at his face and eyes and say goodbye but I was in such shock I just held him the way he liked to be held and rocked him back and forth in the dark. Then they came in, took him from my arms, put him up on the table and inserted the final needle before I was sure what they were doing - and then he was gone… I’ve cried for days.
I was told this would be a peaceful event for my cat, but his last moments were full of pain and terror. It was violent. To be honest, a gunshot to the head would have been more humane! It haunts my memory day and night. I don’t know how to ask the vet and not sound like I am accusing or blaming him. I just want to understand. Why would this happen? Why would the sedative shots be so painful (and why in the muscle)? What would he react so wildly? I don't see much online that this is common. I just want to understand why this might have happened.

Thank you for your reply.

I do wonder about the sedative (how they work). After the second shot made him unable to move (eventually...), he looked right in my eyes for a moment from across the room where he came to lay, then he put his head down and didn't move again. Would he still have been conscious at all? (the room was dark and I couldn't see much so I went and got him and just held him). I wondered if he was too disoriented to know it was me holding him or not?

Thanks so much,

Kim