The most likely cause of toothache is chronic pulpitis. Teeth with pulpitis have different degrees of nerve infection and congestion, and of course, when a person sleeps at night due to lying down, it will lead to blood flow back to the head, which will make the pulp congestion even more serious, and the pressure inside the pulp cavity will increase, which will lead to a toothache that is even more severe than that in the daytime. If you have a tooth with chronic pulpitis, you should seek medical attention in time to have a root canal treatment done on the tooth to remove the infected tooth nerve, rinse and sterilize the root canal cavity, and then fill the root canal tightly. After the root canal treatment, the tooth pain at night caused by chronic pulpitis will disappear completely. In the case of chronic periodontitis, patients with periodontitis may also experience hidden tooth pain at night.