Sudden nosebleed in bed may be caused by dry indoor air, nasopharyngeal cancer and bleeding polyp in maxillary sinus. 1. Dry indoor air: if the living environment of patients is too dry at night, it will lead to dryness of nasal mucosa, which may cause rupture of nasal capillaries, and then sudden nosebleed will occur. 2. Nasopharyngeal carcinoma: It is mainly due to the invasion of cancerous lesions to the mucous membrane of nasal cavity or the invasion of blood vessels, resulting in the damage of nasal mucous membrane, which can easily cause the phenomenon of sudden nosebleed in bed. 3. Hemorrhagic polyp of maxillary sinus: as the surface of polyp is in congested state, if the surface of tumor ruptures and bleeds when sleeping, it may lead to the symptom of sudden nosebleed while sleeping. When the phenomenon of sudden nosebleeds occurs frequently, you should go to the hospital in time to check, and according to the actual cause of the disease to choose targeted and effective treatment.