A typical nosebleed is called an anterior epistaxis. It is a common occurrence, and nothing to worry about. A posterior epistaxis, or blood coming from the back of the throat and making its way through the nose, is a much more serious situation. This condition is rare and can be life-threatening.
A posterior epistaxis is caused by the rupture of a carotid-artery aneurysm into the sinus cavity. Predisposing factors include cold weather; dry climates and high altitudes; chronic use of aspirin and other blood thinning medications; rheumatic fever, hypertension, anemia, and leukemia. It is more commonly found in the elderly than in the general population.