Diarrhea; Vomiting; Weak; Found Slumped Against the Wall; Low Potassium; MRI Found Multiple Small Emboli in Brain; thrown more clots; Aphasia; Difficulty Walking; potassium dropped and she went into A-Fib and threw clots; potassium dropped and she went into A-Fib and threw clots; has problems with recent memories; confusion; food sensitivities; This is a spontaneous report from a contactable physician (patient's daughter). An 86-year-old female patient received her second dose of BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE, lot number and expiration date were not provided) at the age of 86-years-old, via an unspecified route of administration on 24Mar2021 at 14:00 at single dose for COVID-19 immunization. Medical history included high blood pressure diagnosed in 1971 (reported as 50 years ago) and ongoing; type 2 diabetes in 2011 (reported as 10 years ago) which resolved in 2019 (about 2 years ago) after the patient lost some weight; she had an episode of A-Fib in 2019 when her potassium was low (lower than the current hospitalization), once the potassium was corrected, her A-Fib resolved. The physician stated that patient has shrunk and was now about 5 foot 2 inches. Clarified that this has not recently occurred since the vaccine; stated it was happening just with age. The patient received her first dose of BNT162B2 (PFIZER-BIONTECH COVID-19 VACCINE, lot number and expiration date were not provided), via an unspecified route of administration on an unspecified date at single dose for COVID-19 immunization. The patient's concomitant medications were not reported. The patient did not have any issues with the first dose of the vaccine. She received her second vaccine dose on 24Mar2021. The physician spoke with the patient on Friday, 26Mar2021, and the patient was fine. On Saturday, 27Mar2021, the patient had an episode of diarrhea, vomiting and was weak. The lady cleaning the patient's house found her slumped against the wall. The physician met them at the hospital and said the patient seemed okay. They thought it was just an issue from her potassium being low on Mar2021, so they gave her that. The hospital did a CT scan that showed nothing on Mar2021. The hospital did an MRI of the head that showed multiple small emboli in the brain on Mar2021. The physician believed that the patient must have thrown more clots because she became aphasic on Mar2021 and could not name things. The patient also had difficulty walking on Mar2021. The physician felt it was important to call and report this since she has heard of people throwing clots with vaccines. The physician did not know if the events were related to the vaccine. The patient was in the hospital for 7 days (as reported). She was now able to walk with some assistance. The patient's son thought that the patient was okay when he went to see her. Since the reporter was a physician, she knew which questions to ask the patient and saw that she still had some problems. The patient could remember some things but has problems with recent memories on an unspecified date in 2021. She also has some confusion on an unspecified date in 2021, such as she thought she was in a boat hospital. The physician was uncertain if the vomiting and diarrhea was somewhat better. They were wondering if the patient has some food sensitivities (2021). The patient also had carotid studies done in the hospital on Mar2021 and they were fine. They believed that patient's potassium dropped, and she went into A-Fib and threw clots on Mar2021. The clots must have come from the heart valves since the carotid studies were fine and if the clots had been in her legs, they would've gone to her lungs not to her brain. The patient underwent lab tests and procedures which included CT scan: negative, potassium: low, carotid studies: fine, MRI of the head: multiple small emboli in brain, all on Mar2021; and potassium: low, height: 5 foot 2 inches (shrunk), and weight: lost, all on an unspecified date. The events diarrhea, vomiting, weakness and fall required emergency room visit. The outcome of the event difficult walking was recovering and unknown for all other events. The events diarrhea, vomiting, weakness, fall, potassium low, cerebral embolism, thrombosis, and "potassium dropped and she went into A-Fib and threw clots" were assessed as serious due to hospitalization and being life threatening; and the events aphasia and gait disturbance were assessed as serious due to hospitalization. All other events were non-serious. The patient was hospitalized from 27Mar2021 until 02Apr2021.   Information about the lot/batch number has been requested.