In the early stages of pulmonary embolism, symptoms such as difficulty breathing, chest tightness, shortness of breath, and decreased oxygen saturation can occur. Early signs may include chest pain, as chest pain is often an initial symptom of pulmonary embolism. Sometimes the pain can be severe, and some patients may experience coughing, dry cough, and even cough up blood. There may also be symptoms of short exhalation and difficulty breathing, especially in patients with main trunk blockages, where the difficulty in breathing can be very pronounced. In more severe cases, some may experience fainting, suddenly collapsing while walking.