Why do people with kidney failure start shaking and having a fever & vomiting all of a sudden?

Renal failure. The shaking can be due to infection - failing kidneys make you more susceptible to infection. It can also be due to your blood salts being abnormal. This weblink is a good one to find out about the symptoms of renal failure: http://www.Livestrong.Com/article/168915-kidney-disease-symptoms-pains/. Reading this should give you a better understanding of what happens when kidneys fail.