Syncope or fainting is usually caused by a sudden drop in blood pressure. This can happen from bending or stooping for a long period and then standing suddenly. The blood drains from the head and you experience dizziness and sometimes nausea. Your breathing can be affected by anxiety triggered by the event. The treatment for simple fainting is to have the person lay down and if the legs are ok, raise the legs aporox 12". If the person does not feel better in a few minutes call 911.
The episode of syncope in reference to breathing is called Ischaemic episode. This includes the processes that cause normal symptoms of fainting like having a pale skin, rapid breathing, nausea and general weakness of the limbs, in most cases of the legs. The episode response is triggered by insufficient supply of oxygenated blood in the brain. Get more on http://en.wikipedia.org/wiki/Syncope_(medicine).