Normally daily 1-1.5 lt. secretion is produced in sinuses and nose caves and these flow through our nasal passage via various channels and ways and swallowed.  If the quantity of this secretion increases (allergy, sinusitis, condition when the nose cartilage curvature touches the flesh) or the normal quantity while passing through our phanix because of the spoiled receptors in the throat in relation with pharyngitis; false reception detects it as a nasal flix. Treatment is intended to the cause.