Lying down toothache stand up good mainly because of pulpitis, the change of body position caused by changes in the pressure of the pulp cavity, stand up the pressure of the pulp cavity is relieved, so the toothache is relieved. Lying down toothache stand up well mainly because of pulpitis. The pulp is located right in the center of the tooth, wrapped in thick dentin and hard enamel. The reason why you feel pain in pulpitis is because when the pulp is inflamed, the pressure in the pulp chamber increases and the nerves become painful. The change in body position causes a change in the pressure in the pulp chamber, which becomes greater when you lie down. When you stand up, the pressure in the pulp chamber is relieved, so the toothache is relieved. It is recommended that you consult with your medical professional.