Sudden nosebleeds in the middle of the night in adults may be caused by dry rhinitis, nasal capillary hemangioma, hypertension and so on. 1. Dry rhinitis: if the living environment is too dry, along with the mucous membrane of the anterior part of the nasal septum, there are erosion and superficial ulcers, which may increase the risk of capillary wall rupture due to the relative decrease of nasal secretion at night, and then sudden nosebleed in the middle of the night under the stimulation of the dry environment. 2. Nasal capillary hemangioma: if there is a case of nasal capillary hemangioma, nosebleed may occur due to the rupture of the tumor at night. 3. Hypertension: If hypertensive patients do not take antihypertensive drugs on time and according to the dosage, resulting in poor control of blood pressure, so that the blood pressure for a long time in a relatively high state, it is easy to cause capillary rupture in the nasal cavity, thus appearing in the middle of the night sudden nosebleed. If you have a sudden nosebleed in the middle of the night or if the bleeding does not stop, you should consult a doctor in a timely manner to clarify the cause of the bleeding and standardize the treatment, so as not to delay the condition.