Yikes you have been bitten 4 times and survived! I am glad you are still here.
You are the perfect person to ask this question. I was hunting with MrD. I got down from the tree I was sitting in to walk back to camp. I surprised a rattlesnake coming down the path toward me. He was a small snake, not much over 3 feet. I heard him rattle, buzz was more like it.
Then he jumped up on his tail and started wiggling around. He was totally upright with his tail bouncing around on the ground.
He continued this action until I started shooting.
I know this happens because I have seen an old painting, either Russel or Remington that pictured snakes doing this during some kind of Indian ceremony, but I have never talked to a person who has seen it.
Never seen what your describing but I have seen them in the standard s curve defensive position and in the vertical mating dance position where they do get vertical but still have at least 50% of their body laying flat.
http://www.youtube.com/watch?v=uNXe79MKXQk