This is why they asked me to cough after an angioplasty procedure where my heart rate kept increasing and my BP was very high. Unfortunately I couldn't cough due to nausea and they had to resort to medications.
This is very common and is a result of your vagus nerve being stimulated by the coughing resulting in a sudden drop in blood pressure as it temporarily causes your heart to pump less efficiently causing less blood to go to your brain. The drop in BP causes your symptom of feeling faint, it is very common and completely normal.
Jon