Yeah that's true that the actions of these systems while the body was coping with stress surpressed the function of the immune system, hence leaving the body more vulnerable to disease BUT, the nervous system helps because the PARASYMPATHETIC system of the autonomic nervous system kicks in to calm the body down and restore it back to it's normal physiological levels (allowing it to continue to stay less vulnerable to disease again). Im' guessing the cortisol is withdrawn or something, i don't know haha.