That typically means that your blood pressure is too high. The nose membrane is very thin and if your blood pressure is high it will keep flowing.
hang your head over the sink and let it flow till it's done...you won't die...place a cool wet towel over your head and breathe and relax. If it hasn't stopped after ten minutes of that take a paper towel and dip it in vinegar and put it the problem nostril. It will cause the membrane to contract and seal...it will feel a little strange.
You're welcome.