Hi welcome to health caremagic I have gone through your query. The blood clot in saliva is most common because of the gum infection. When the gums are infected then the gums will enlarge and starts bleeding. This will be more common in the morning time & during Brushing. In case of throat or lung infection blood comes mixed with mucus & after coughing. Consult a oral physician/dentist and scaling or cleaning may be required. In meanwhile, You can use topical gum astringents like gum paint & metronidazole 400mg twice a day for 3 days. You could also use mouthwash like Listerine Don t worry you would be fine Hope my answer Helps