Waking up in bed with blood in your mouth is usually the result of periodontitis, but you also need to be alert to systemic diseases, as described below. 1. Healthy gums, even if a little hard brushing or gingival groove probing will not cause bleeding, in the early inflammation of the gums for gingival groove probing bleeding, the patient often in the brushing or biting hard objects bleeding, with the development of the disease will appear spontaneous bleeding, and then woke up to find that there is blood in the mouth. 2. Bleeding is caused by capillary expansion and congestion in the connective tissue of the gingiva, and the epithelium in the sulcus can be interrupted by the continuity of the ulcer, and tiny stimuli can cause the capillaries to rupture and bleed. Sleeping wake up with blood in the mouth may have other reasons, such as blood system diseases, etc., it is recommended to go to the hospital in time to find out the cause of the disease after receiving regular treatment.