What Causes High Heart Rate Along With Dizziness?

Hello, about 30 mins ago I could feel my heart beat speed up. I checked it 3 times for the average at 94 bpm. I felt a little light headed and woozy. Now I have checked my rate again (30 mins later) and I m lower at 75bpm. My normal resting rate is around 82. I have taken a Benadryl around 10am tiday because for the past 6 days I have been breaking out with hives. Just wondering if I should be consumed at this point or if it s normal.