Periods of Heart Racing

Hello,

Four years ago my cardiologist diagnosed me with Inappropriate Sinus Tachycardia. Up until October, on medication I rarely had a racing episode that lasted for more than half an hour. Since October of last year, I have been having periods of heart racing that last for a few days to a few weeks where my average resting heart rate will be at least 120 beats per minute. This is on 300 mg of Tiazac. When I'm not having these periods, my average resting hr is in the 80s and 90s, so my cardiologist is happy with the way the medication is working.

1. What could be causing my heart to race for such extended periods of time?

2. Is there anything I can do to alleviate the fast heart rates since my cardio doesn't want to increase my medication?

3. Can these periods of heart racing signal a non-heart related problem?

4. My heart sometimes beats at 130 to 140 beats per minute for several hours. Do I need to go to the hospital for this?

Thank you so much.