Sudden onset of breathlessness is considered to be caused by the following reasons: 1. Acute attack of bronchial asthma, such patients are mostly due to exposure to allergens, resulting in an acute attack of symptoms. It is recommended to check lung function, allergen test, excitation test and diastolic test for clear diagnosis; 2, acute pharyngitis, this kind of patients are mostly due to acute inflammation and allergy, resulting in acute edema of the larynx, and sudden onset of symptoms of feeling unable to get air and difficulty in breathing, it is recommended to check laryngoscopy, blood count, etc. for clear diagnosis; 3, pulmonary embolism, this kind of patients mostly occur in patients with Patients with bilateral lower limb vascular lesions, post-surgery, post-trauma, etc., mostly accompanied by hemoptysis, dyspnea and other symptoms, and it is recommended to check D-dimer, blood routine, pulmonary angiography and other tests to clarify the diagnosis.