Waking up with blood in the mouth may be caused by oral injury, inflammation, blood system diseases or long-term use of certain drugs, which need to be checked in the hospital. 1. Trauma. Sleeping in the mouth if there are sharp tooth roots or bad restorations, may scratch the oral mucosa triggered oral bleeding. 2. Inflammation. Severe periodontitis or long-term chronic periodontitis can lead to blood oozing while sleeping. 3. Blood system diseases. Leukemia and other blood system diseases gum margins are prone to bleeding. 3. Long-term medication. Cerebral thrombosis, heart attack and other patients will take anticoagulant drugs for a long time, also easy to cause oral soft tissue bleeding. Waking up with blood in the mouth specifically need to go to the hospital to check the cause of blood seepage and timely treatment.