I received a dose of the Pfizer Bivalent booster on 9/11/2022. On the morning of 9/12/2022, I woke up feeling kind of like I had a moderate case of the flu. I had a headache, body aches, and a slightly elevated temperature. That morning, I just sat on the sofa doing nothing when I noticed that I had a fluttering sensation in my chest. My Apple Watch informed me at the time that I had had a resting heartrate of around 148-156 for the past 10 minutes. The Apple Watch instructed me to put my finger on its crown to test for atrial fibrillation, which I did, and it indicated that I indeed had atrial fibrillation. I waited for a while and then I checked for atrial fibrillation again, and it indicated that I was still experiencing atrial fibrillation. The atrial fibrillation continued for at least 4 hours. Later that day, I went back to bed. I slept for about 5 hours. When I woke up, I tested myself again, and my resting rate was still slightly elevated, though it was closer to my normal rate; my resting heartrate is usually in the 70s, but it was in the 90s at this point. Also, the Apple Watch indicated a normal sinus rhythm, so I wasn't having any atrial fibrillation at this point. For the rest of the evening of 9/12/2022, I continued checking myself for elevated heartrate and atrial fibrillation. It remained somewhat elevated (in the 80s), but I didn't experience any more fibrillation. On 9/13/2022, everything was back to normal. On 9/19/2022, I was sitting in a relaxed position when I felt the fluttering sensation in my chest again. I checked my resting heartrate on my Apple Watch again, and it was in the 140s. I checked for atrial fibrillation and it was also indicated. I called my doctor and set up an appointment for the following day, but by the time my appointment rolled around, I was no longer having fibrillations, so my doctor could not witness what I was describing. However, he did see the readings of my Apple Watch on my phone, so he prescribed me Bystolic. He instructed me to take it if I had more fibrillation. I did not have any more issues until 9/27/2022. Once again, my heartrate was in the 140s and atrial fibrillation was detected. I took the Bystolic, and everything returned to normal within 3 hours. On 9/28/2022, the fibrillation recurred. I took the Bystolic again and saw my doctor to see if it would be safe for me to travel, as I was planning a trip abroad on 10/3/2022. The doctor told me that I should take the Bystolic with me on my trip and that if the fibrillation recurred, I should begin taking the Bystolic daily while I was on my trip. On 10/2/2022, my heartrate was again in the 140s-150s. In addition to this, my systolic blood pressure was 126 and the diastolic pressure was 110. I found this concerning, especially since I was due to catch a flight the following day, so I went to the ER. Although I had already taken a Bystolic by the time I got to the ER, it was confirmed by the staff that I was still having atrial fibrillation. They did an EKG, a chest X-ray, thyroid hormone test, troponin test, D-dimer test, a CBC test, and complete metabolic panel. They concluded there were no structural issues with my heart, but that I had issues with my electrical system. They told me that it was safe to travel as long as I took my Bystolic during the trip. They also instructed me to not panic if another episode took place. Instead, I was to take the Bystolic and wait until it passed. I took the Bystolic with me on the trip and I took one pill on the day of my flight. I had no issues during the flight. I was at my destination for 9 days. I didn't take any more Bystolic during my trip, though I did periodically check my Apple Watch, and all indications were that my heartrate was fine. At the time of this writing, it has been 10 days since I last had an atrial fibrillation episode and 9 days since I have taken Bystolic, and everything is fine, so far.