Your heart rate is a reflection of multiple factors, and in the case of AF, most frequently , but not all the time, it is due to sympathetic overtone that releases extra adrenaline which in turn increases your heart rate ( this is provided that your heart has normal function and has been fully investigated conventionally).

Too fast a heart rate is not good, no matter what the cause it. Some people , however, have very fragile heart rate that is very sensitive to stressors and it can go up and down. It can be scary and warrant visit to the ER for check up. There is usually a underlying cause. Something in your life may be triggering. It can range from wrong food such as wheat or diary or sugar, or stress, or exposure to EMF, just to name a few. Some people get triggered just by entering a store with florescent light. The more sensitive your body , the easier it is to get triggered. Other times, the body needs some time to settle down after crash, and this can occur and is part and partial of the recovery process. We do see it clinically and a careful history to eliminate the reasons is necessary. Its a lot of detective work.

Sympathetic overtone can be reduced if you do Adrenal Breathing Exercises properly. Taking it easy and have a balanced life is always a good thing. Most people with high level of adrenaline sensitivity also have some history of suppressed or repressed rage sometime in their life , perhaps childhood, that warrant a detail self examination.