As strange as it sounds when you are crying a little bit you just have a few tears, but when you are crying and crying you have tears and a runny nose. You get the runny nose because the extra tears go into the nasolacrimal ducts at the corner of your eyes then run into sinus.
it gets runny because when you cry tears come out of the tear glands and drain through the tear ducts that empty into your nose..and that is why it runs