In other words, the body shuts down. In order to preserve itself, it implements across-the-board reductions in energy output. The crucial point to remember is that doing so ensures survival of the individual in a time of extreme stress. Yeah, you might feel lousy, but you’ll live to tell the tale. Reducing output is the smart thing for the body to do. Burning energy it does not have would quickly lead to death. The energy budget must be balanced.