When acute pulmonary embolism occurs, it is primarily due to a thrombus from the venous system being carried by the venous blood flow back to the right heart, and then due to the ejection from the right heart, this thrombus gets lodged in the pulmonary artery, forming a pulmonary embolism. After the onset of pulmonary embolism, the primary treatment measure is to have the patient lie down and remain still. The reason is mainly that if the patient is standing or moving, it is very likely that the thrombus in the venous system could continue to detach and move within the venous system. This can worsen the symptoms of pulmonary embolism or lead to new embolic sites, so the treatment for the patient involves immobilization and lying down to avoid further movement, making this the most basic approach to treatment.