 Several conditions , including Parkinson 's disease , diabetes and so @-@ called pure autonomic failure , can cause a loss of norepinephrine @-@ secreting neurons in the sympathetic nervous system . The symptoms are widespread , the most serious being a reduction in heart rate and an extreme drop in resting blood pressure , making it impossible for severely affected people to stand for more than a few seconds without fainting . Treatment can involve dietary changes or drugs . 
