Oral trauma, post-nasal drip, coughing up blood, gastrointestinal distress, oral cancer, narcotics use and infection can all cause blood to pool in the mouth. Trauma is an extremely likely scenario because it is possible to bite the tongue or cheeks while sleeping. Gingivitis, or gum disease, can also cause the gums to bleed, according to MD-Health.
Post-nasal drip or a nosebleed are also likely sources of blood in the mouth upon waking. If the nasal passages become irritated, blood can drip into the mouth, resulting in blood in the saliva. Coughing while asleep can also result in blood from the lungs or gastrointestinal tract making its way into the mouth.
Certain narcotics, such as crystal meth, result in oral lesions that might bleed overnight. Some medications might also cause the gums and other oral tissues to bleed, which is why it is important to discuss this symptom with a physician, according to HealthHype.
Infections, including bacterial and viral infections, can also cause blood in the mouth upon awakening. Yeast infections, for example, can occur in the mouth.
Certain types of cancer can result in bloody saliva, including esophageal, stomach or lung cancers or lymphoma.
While bloody saliva rarely signals a serious medical condition, only a doctor can provide a definitive diagnosis for blood in the mouth, states MD-Health.