I had to petsit a dog once, and he needed allergy shots. I was 14, well on my way to becoming an exotic pet veterinarian! It was fine, although one time he moved the needle got in my skin like half a millimeter. I freaked out, but nothing happened and I was okay!
I could not imagine giving my poor snake a shot! And although I feel bad for your snake, livinggoddity, I kind of laughed at the description of him hiding in your hair after being probed!