They do not occur with every sex act. Some people go for years between episodes. Obviously, sex raises the blood pressure. This in turn raises the pressure in the head. Also, sex causes muscle tightening and tension.
Sex headaches are a combination of the blood pressure and muscle tension, for most people.
Some cases have been found where there is low pressure of the fluid around the brain and spine. In rare instances, sex headaches unveil underlying medical problems. The doctor will review all her symptoms and neurological signs in the office. A spinal tap is done rarely. Once they occur, the treatments are much the same as any headaches.