dear Therese,
it is normal to produce approximately 100ml of secretions in a day on an average. of course provided there is no underlying physiological causative agent like an irritant/ drug intake.. etc... you will find more in a book called Egans, also any basic book on physiotherapy in cardiopulmonary rehabilitation by Randall Braddom or even Hillegass or best recomended would be Scot Irwin.
have you evr tried taking lots of coffe/ standing near a heap of waste burning?... forget it all ever had a runnig nose? well its all the same ; incerased secretory reactions to a stimulus... read more on response to sympathetic and parasympathetic stimuli on the endothelial system.. basic physiology.
hope you find these books...
happy reading
kripag