When you mentioned your cat having a burst of energy when the shot was administered, it reminded me that my Angel did the same thing. The vet told me that first they were going to administer the sedative by means of a shot. He said that it burns and to expect the cat to react
From that. They had to put a towel over her head to prevent her from biting. After that, they inserted an introvenous needle for the actual drug. So maybe your cat was reacting fron the sting of the sedative?
I will wait patiently for a visit from her.