Waking up in the middle of the night with blood in your mouth can be caused by conditions such as chronic gingivitis, gastrointestinal bleeding, and lung disease. 1. Chronic gingivitis: chronic gingivitis can lead to tissue edema and thinning of the gum tissue, which can rupture and bleed after sleeping under the action of the teeth and oral muscles, resulting in blood in the mouth. 2. Gastrointestinal bleeding: ulcers or acute mucosal injuries can cause bleeding in the gastrointestinal tract, and blood can be spit out after too much bleeding. 3. Lung diseases: bronchodilatation, bronchopneumonia, tuberculosis and lung cancer and other lung diseases can cause lung hemorrhage, rupture of blood vessels in the lungs will cause blood to enter the lung tissue from the blood vessels, and then flow into the mouth with breathing. After the occurrence of waking up in the middle of the night with blood in the mouth, you should go to the hospital in time, ask the doctor for a clear diagnosis and treatment, do not ignore or self-treatment, so as not to delay the condition.