She was so dizzy; Stool black; Explosive bowel movements; hot and cold chills; hot and cold chills; drenched in sweat; walker to back up in the bed; Nauseous; Sore arm; Slight headache; This is a spontaneous report from a contactable consumer (the patient). A 69-year-old female patient received the first dose of BNT162B2 (PFIZER-BIONTECH COVID-19 MRNA VACCINE; Solution for injection; Lot Number: EM9810), on the morning of 16Feb2021 09:58 (at the age of 69-years-old) intramuscularly in the right arm as a single dose for COVID-19 immunization. The patient's medical history included knee replacement surgery years ago, dyslipidemia, depression,  insomnia, constipation problems; she was taking clopidogrel (PLAVIX) because she had a hole in her heart last year (2020). This was fixed (on an unspecified date), and she was only taking PLAVIX once a day for one year, which will be until Jul2021; the patient called it a hole in her heart because that was what her heart specialist told her. Concomitant medications included: clopidogrel bisulfate (PLAVIX) taken for hole in heart from Aug2020 and ongoing, venlafaxine hydrochloride (EFEXOR), simvastatin (ZOCOR), and temazepam. The patient had an allergic reaction to sulfamethoxazole/ trimethoprim (BACTRIM), and she was also allergic to hydrocodone bitartrate/ paracetamol (VICODIN). On 17Feb2021, had a slight headache and a sore arm. On Friday, 19Feb2021, she woke up very nauseous to her stomach; no treatment received. The patient had hot and cold chills really bad. Her head was just drenched in sweat and this occurred all day long. When she did go to use the restroom and had a bowel movement, her stool was black. It was like black tar around 10:00 or 11pm, it was bad. Every time she sat down to use the bathroom, the sweating would get more intense and every time she would get up and use the restroom, she had to use a walker. Then, she used the walker to back up in the bed (19Feb2021), and she seemed to be okay. It seemed like the sweats would go away and she would get the cold chills. The patient just put a heating pad on her stomach, and this occurred all day long until Saturday morning. She mentions she does have constipation problems, but this was explosive. She couldn't get to the restroom a few times. She had several explosive bowel movements on 19Feb2021 10:00. Her husband brought the garbage pail in the bedroom and she did use plastic on the bedding. By 11:30-12pm on Saturday (20Feb2021), it completely stopped, but she was still sweating. She was so dizzy. It would hit her so bad and her head as wringing wet. However, when she would get back in the bed and lay down flat, the sweating would go away, and she would start to get the cold chills. The patient explained the sweating/hot and cold chills went away by yesterday afternoon (unspecified date). She was able to walk back and forth to the restroom with no problems. She verified all of her symptoms have improved. On 02Apr2021, the patient reported she received the second dose of the vaccine on 09Mar2021. The patient reported that sore arm and chills were important medical events, for which no treatment was received. Treatment received for diarrhea included "limgen". The outcome of explosive bowel movements and stool black was recovered on 20Feb2021, and the other events recovered on an unspecified date.  Follow-up (02Apr2021): New information received from a contactable consumer includes: medical history, product data, concomitant medications, and event details. Case upgraded to serious.   Follow-up attempts are completed. No further information is expected.