There are many reasons for this condition: First, the most common reason is oral problems, such as gingivitis, calculus, periodontitis patients, after a night of sleep, the oral mucosa will bleed, and in the morning when you get up you will find blood in your mouth. Second, blood system diseases caused by, for example, platelet reduction or some patients have coagulation disorders, blood clotting problems will also appear in the mouth with blood. Third, blood comes from the respiratory tract, for example, some patients have bleeding in the nasal cavity when they sleep, and blood flows from the nasal cavity to the mouth through the throat when they sleep, and bleeding is found in the mouth when they wake up in the morning. Fourth, diseases of the digestive system, for example, some patients have upper gastrointestinal bleeding and may find bleeding in the mouth.