Shivers = Negative Energy
In yoga, or even to simply remain calm.. we are told to take deep breaths. I believe that "taking a deep breath" is the easiest way to get someone to "shed their negative energy". The reason I believe this is because if you take a full breath, it is quite difficult to NOT feel the chills you describe. I noticed personally that (no matter how I do it) when I activate these chills.. I very quickly become more calm and happy. Any anxiety or anger that I am experiencing will be greatly reduced after feeling these "chills". I've grown to believe that this is "shedding your negative energy". The chills are a result of actually FEELING the energy leave your body. I get my best result after a nice breath, eye's closed and rolling my shoulders.. the sensation is in my shoulders, upper spine, neck and also a bit in my lower back.
We are all capable of complete control, we just need to accept, learn and practice.