Covid 19 vaccine exacerbated her chronic fatigue syndrome; Covid 19 vaccine exacerbated her chronic fatigue syndrome; atrial fibrillation; tachycardia/ heartrate got was 222 beats per minute; missing heartbeats; chills; fever; fatigue; lethargic; felt crummy; This is a spontaneous report received from a contactable consumer (patient). A 72-year-old female patient received the first dose of BNT162B2 (PFIZER COVID 19 VACCINE), via an unspecified route of administration, administered in Arm Left on 13Apr2021 15:00 (Batch/Lot number was not reported) at age of 72 years as single dose for covid-19 immunisation. Medical history included ongoing chronic fatigue syndrome at age 32 (she had been doing natural therapy and had gotten herself to a stable period but her chronic fatigue syndrome was still an issue sometimes), atrial fibrillation (had been admitted to the hospital because of it, she was not admitted to the hospital when she had atrial fibrillation after receiving her Covid 19 vaccine). The patient's concomitant medications were not reported. Historical vaccine included the first flu vaccine she every received sent her over the moon. Clarified she was in bed sick after receiving the flu vaccine. Patient was calling because she didn't do well with her first Pfizer Covid 19 vaccine. After the Covid 19 vaccine she experienced chills and fever on 13Apr2021 for a couple days. Then she had fatigue on 13Apr2021and that was a few days of her own chronic fatigue syndrome flaring up. She also had some problems with her heart like atrial fibrillation and tachycardia on 18Apr2021. She saw her cardiologist and he wanted her to do the dye stress test where she ran on the treadmill. The day her stress test was scheduled was the same day as her second Covid 19 vaccine. She was calling to find out if she can get the dye at her stress test and run on the treadmill and get the Covid 19 vaccine on the same day. Or does she need to put the stress test off for a couple weeks. She felt like the dye from the stress test and the Covid 19 vaccine might be too many chemicals in her body for one day. She felt like the Covid 19 vaccine exacerbated her chronic fatigue syndrome. She reported that something as simple as to much sugar or to much sun or exertion can also exacerbate her chronic fatigue syndrome. She was prepared in her thinking that the Covid 19 vaccine would be difficult for her because of her history with chronic fatigue syndrome. She had chills and a fever for a few days after the Covid 19 vaccine. She did not take her temperature to get a recorded number. She was lethargic and really felt crummy on 13Apr2021 for about the first 3 days. On day 4 she was better. Then the heart stuff started. Clarified, the atrial fibrillation and tachycardia started. She took medicine as needed for her atrial fibrillation and tachycardia. She had the atrial fibrillation and the tachycardia for about 3 days in a row. She reported she was stable now. She was able to monitor her heartrate on her watch. She then printed out her heart rate readings from her  watch to take to her doctor. The highest her heartrate got was 222 beats per minute and that happened a couple times. Her watch only showed her heart rate as 150 beats per minute but when she printed the information it showed her true heart rate. She did see an electrophysiologist before she received her first dose of the Covid 19 vaccine. She was preparing herself for if anything was going to go wrong when she received the vaccine, she wanted to know what to do. She wanted to prepared in case the Covid 19 vaccine caused her any trouble. She was prescribed Diltiazem by her cardiologist to take as needed when she was having the tachycardia and atrial fibrillation. She was taking 15mg three times a day on the three days that she had the atrial fibrillation and tachycardia and it helped. She received her first dose of the Covid 19 vaccine on 13Apr2021 and according to her watch she started missing heartbeats on 14Apr2021. The atrial fibrillation and the really bad heart stuff started on 18Apr2021 and went on until 22Apr2021. She would say her heart issues started to resolve on the afternoon of the 22Apr2021. She was still missing heart beats according to her watch but nothing bad. She saw her cardiologist on Friday, 23Apr2021 and at that appointment she was in normal sinus rhythm. She has had some ups and downs since the 23Apr2021. Her second Covid 19 vaccine was scheduled for 04May2021 at 11:00AM. She did have a 3D echocardiogram and based on that, the doctor wanted to rule out any blocked arteries and that's why she's doing the stress test. AEs (atrial fibrillation and tachycardia) require a visit to Physician Office. Outcome of events chills, fever, lethargic, felt crummy was recovered on 17Apr2021, and the other events was unknown.