text: why do we tremble when having a cold? i have a not so severe cold meaning i get runny nose once in a while but i do see to be cold at times n hot at other times, y is this happening?? is a way for the body to fight off infections?? or am i just understanding this all wrong!! while some of the above answers have slight truths to them…these are the anatomic (real medical) reasons why this happens.  everything you described happens because when you get an infection, our body naturally tries to fight it off.    when we get a fever our bodies try to kill the infection by turning up our internal temperature.  bacteria and viruses cannot live at high temps and are killed by our fever.  this is when we feel hot.    our bodies respond by shivering to raise the temperature. shivering produces heat in the body. once the temperature goes up, we start to feel warm. when the fever goes away, that is when we sweat  you get a runny nose, because your body decides to make extra mucus in order to “wash” away any bacteria that could get trapped in your sinuses.  i hoped that helped...i tried to get to the point and not be so “wordy”