When you have a fever your environment feels relatively colder due to your higher body temperature. Your body tries to keep you from getting cold, so it shivers to raise your internal temperature. It is all done by your hypothalamus, which is your body’s thermostat. When your body is invaded by germs, the hypothalamus detects your body’s immune response and raises the temperature setting in your body to help kill the germs, many of which only thrive at normal body temperature. In order to generate the extra heat your body may shiver as a way to increase your internal temperature. When your muscles work your body temperature goes up. Shivering is your muscles contracted and relaxing very quickly. Basic physics dictate that energy taken from a storage source (like our fat) and changed to another form of energy (your body movements), results in yet another form of energy – heat. So when your muscles start moving back and fourth rapidly, they make heat,