Of those presenting with syncope to an emergency department, about 4% died in the next 30 days. The risk of a poor outcome, however, depends very much on the underlying cause. Situational syncope is not at increased risk of death or adverse outcomes. Cardiac syncope is associated with worse prognosis compared to noncardiac syncope. Factors associated with poor outcomes include history of heart failure, history of myocardial infarction, ECG abnormalities, palpitations, signs of hemorrhage, syncope during exertion, and advanced age.
complications of Hyperventilation
complications of Aspiration pneumonia
complications of Hypoxia 
complications of Carbon monoxide poisoning
complications of Bad breath
complications of Bronchiolitis
medical cause of Pulmonary insufficiency
complications of Air embolism