What Causes Elevated Heart Rate And Palpitations While Suffering From SVT?

Around 13/14 years old I was diagnosed with SVT (Superventricular tachycardia) , when it first happened it would last several minutes and by the age 15 it was down to a few seconds (10-15), I ve seen a cardiologist and at the age 15 svt was so irregular they said I don t have to go for check ups anymore unless something happened again. I m now 17 and have only had palpitations, recently, also everytime I stand up my heart rate seems to go straight up causing me to get light headed for a few seconds, and make me feel a bit out of breath. What I would really like to ask is recently I was playing skirmish outdoors, I was running around for about 30-40 minutes, we decided to have a short break and as I was walking, I noticed my heart was going so fast I couldn t even count, I alsocouldn t catch my breath at all I tried deep breaths and still couldn t breathe, then suddley everything started turning black and I could barely see I had to hold onto a bin and I was sure I was going to faint any second, my heart still racing I barely walked to a chair it took about 20 minutes for my heart to slow down. For the rest of u day and the following 2 days I felt weak for example I felt as if my heart rate was higher than normal, and a thumping in my chest. Should I have gotten help at the time? What are svt emergency ancy symptoms?