Continuous bleeding always requires a dentist's intervention. A would bleeding again a few hours after a surgical procedure can have various causes: light bleeding 2-4 hours after the procedure is usually due to the anaesthetic wearing off, which often contains a vascoconstrictive ingredient.
If the bleeding starts again after more than 12 hours, this can be due to wound healing disturbances. They can occur due to an immunodeficiency or due to the patients behaviour. This means the body is unable to form a blood clot in the wound, or it has dissolved. Reasons can be physical exertion, exposure to sunlight, or too extensive rinsing of the wound.
Blood thinning medication like Aspirin or Marcumar also commonly cause secondary bleeding. Aspirin should generally be avoided as a painkiller after surgical procedures. If you are taking these medicines to regulate cardiovascular function, please consult your GP before interrupting intake.
In all cases avoid physical exertion as well as consumption of caffeinated and alcoholic drinks. Bleeding can often be stopped through compression of the wound. Tie a knot into cloth, lay it on the wound and bite on the knot for about 30 minutes. If you cannot stop the bleeding like this, consult your dentist.
Stay calm! Any secondary bleeding after dental surgery is minor in most cases and not dangerous. The blood mixing with saliva can also give the impression of more blood than it actually is.