Sams symptoms and conditions

Was prescribed prednisone 10mg dose pack. Took my first days worth and by bedtime my heart was beating so fast it felt as if it was going to pop out of my chest and burst. I went to the hospital and per the doctors there, SVT is not a reaction to prednisone. Anyways, left hospital with a clear bill of health, heart was in good condition.
Now, If it wasn't the prednisone that caused this rapid heart beat, what was it? I really think that the prednisone was the cause but as long as I'm not sure, I fear this will happen again out of the blue.