What could cause bleeding to death?

Many causes: A severed artery or big vein, a ruptured organ most notably the liver, an ulcer or cancer causing bleeding into the gut, lack of platelets causing bleeding from the rectum, esopageal varices from liver disease that rupture and cause fatal vomiting or passage of blood -- all these and many others. The dying person feels primarily a sensation of cold; if you've lost someone you have my sympathy.