I think that is a great question for your doctor. Mayo Clinic has some information on diagnosing Supraventricular tachycardia and the tests used here: https://www.mayoclinic.org/diseases-conditions/supraventricular-tachycardia/diagnosis-treatment/drc-20355249

Hello Ashleigh - that must have been frightening. I am not a doctor, but I will try to explain in layperson terms the way my daughter has explained it to me. She is an RN who teaches Advanced Cardiac Life Support to nurses and first responders.

When you are in SVT, the rapid heartbeat may not be filling all chambers of the heart, therefore insufficient blood is being pumped out of the heart and into the body. Tachycardia can cause very low BP, and the "flutter" may make it difficult to measure.

SVT is an indication of an electrical problem in your heart. Sometimes it is a one-time or rare event, perhaps brought on by stress, too much caffeine, medications, street drugs or smoking. Other times, it may be caused by a hereditary flaw in the wiring of your heart. Tests will determine the exact type you have and whether/how it needs to be treated.

Have you been instructed what action to take if it happens again? Do you have family members with heart issues?
Sue