Some causes of a sudden nosebleed include trauma to the outside or inside of the nose, the inability of the blood to clot, certain diseases and abnormal blood vessels, states WebMD. Most nosebleeds are not serious.
There are two types of nosebleeds: anterior nosebleeds and posterior nosebleeds, according to WebMD. Anterior nosebleeds are the most common, accounting for more than 90 percent of all nosebleeds. The bleeding comes from a blood vessel near the front part of the nose. Posterior nosebleeds are less common and originate in an artery near the back of the nose. These types of nosebleeds typically require a hospital visit.
Nosebleeds occur especially in cold, dry climates and winter months, notes WebMD. Nosebleeds are most common in children under 10 and the elderly.