I was dehydrated/ gave me Magnesium and some sodium and then an IV; low on potassium; I had electrolytes messed up; my head snapped; I couldn't walk; immune compromised; thought I was dying it scared me; also picked up some extra heart beats; I felt my eyes rolling around, I got very dizzy/ dizziness; I end up falling; This is a spontaneous report received from a contactable reporter(s) (Consumer or other non HCP) from medical information team. The reporter is the patient.  A 78-year-old female patient received bnt162b2 omi xbb.1.5 (COMIRNATY (2023-2024 FORMULA)), on 06Oct2023 as dose 1, single (Batch/Lot number: unknown) at the age of 78 years, in right arm for covid-19 immunisation. The patient's relevant medical history included: "Rheumatoid Arthritis" (ongoing); "allergies" (unspecified if ongoing), notes: have various allergies. Concomitant medication(s) included: SIMVASTATIN, start date: 2000; VALSARTAN / HIDROCLOROTIAZIDA, start date: 2020; LEVOXYL, start date: 2022. Vaccination history included: Covid-19 vaccine (Dose 1, Manufacturer Unknown), administration date: Feb2021, for COVID-19 immunisation, reaction(s): "sick"; Covid-19 vaccine (Dose 2, Manufacturer Unknown), administration date: Mar2021, for COVID-19 immunisation; Covid-19 vaccine (Dose 3 (Booster), Manufacturer Unknown), administration date: Dec2021, for COVID-19 immunisation; Covid-19 vaccine (Dose 4 (Booster), Manufacturer Unknown), administration date: May2022, for COVID-19 immunisation; Covid-19 vaccine (Dose 5 (Booster), Manufacturer Unknown), administration date: Nov2022, for COVID-19 immunisation. The following information was reported: FALL (non-serious) with onset 14Nov2023, outcome "unknown", described as "I end up falling"; DIZZINESS (non-serious) with onset 14Nov2023, outcome "not recovered", described as "I felt my eyes rolling around, I got very dizzy/ dizziness"; DEHYDRATION (medically significant), outcome "unknown", described as "I was dehydrated/ gave me Magnesium and some sodium and then an IV"; BLOOD POTASSIUM DECREASED (medically significant), outcome "unknown", described as "low on potassium"; BLOOD ELECTROLYTES ABNORMAL (medically significant), outcome "unknown", described as "I had electrolytes messed up"; HEAD DISCOMFORT (non-serious), outcome "not recovered", described as "my head snapped"; GAIT INABILITY (non-serious), outcome "unknown", described as "I couldn't walk"; IMMUNE SYSTEM DISORDER (non-serious), outcome "unknown", described as "immune compromised"; FEAR OF DEATH (non-serious), outcome "unknown", described as "thought I was dying it scared me"; EXTRASYSTOLES (non-serious), outcome "unknown", described as "also picked up some extra heart beats". The event "also picked up some extra heart beats" required physician office visit. The events "i was dehydrated/ gave me magnesium and some sodium and then an iv", "low on potassium", "i had electrolytes messed up", "i felt my eyes rolling around, i got very dizzy/ dizziness", "my head snapped" and "i couldn't walk" required emergency room visit. The patient underwent the following laboratory tests and procedures: Blood potassium: Low; electrolytes: messed up. Therapeutic measures were taken as a result of dehydration, blood potassium decreased. Clinical Course: She mentioned: The day she got the shot she was fine, she went out to get some dinner and at  5 o' clock, her head snapped, she felt her eyes rolling around, she got very dizzy, she couldn't walk. When she got out of the restaurant she went to the medical walk-in, then she went to the ER (Emergency Room) and 4 hours later and lots of test, they said she was dehydrated, her electrolytes were all messed up, she was low on potassium and they gave her potassium in IV (Intravenous) and magnesium, she got in on a wheelchair and walked out of there. But now, maybe once a week, the last time being last night, it hits all of a sudden, sometimes it feels like her eyes are rolling up and down too fast. But last night she was just finishing dinner and all of a sudden she got very dizzy and she end up falling because she couldn't make it to the bed on time. No one seems concerned about this dizziness, She was afraid to drive. She was on a biologic for rheumatoid arthritis so she went at the two week mark, she got it once a month, one vaccine last month, she wanted to get the flu and the RSV. She had 6 vaccines since 2021, (Feb2021, Mar2021 and that was the first two, Dec2021, May2022, Nov2022). This is almost a year later from the last vaccine, seems like it might have been too much of a good thing and that's what's causing the dizziness. She also have various allergies. The first vaccine she was sick for a day or two, but she took a lot of water, but it was all smooth sailing. She thought she was dying it scared her, went to the cardiologist, they monitored her for a week but she also picked up some extra heart beats. She got another two shots of the biologic, but she was nervous that day that it would cause a problem. She had couple of concerns but she got her last the new launched vaccine, Comirnaty on 06Oct2023 and end up in the ER (Emergency Room) for four hours, she had electrolytes messed up, they said she was dehydrated, all she did is drink water. They gave her Magnesium and some sodium and then an IV (Intravenous). She came home and she was okay but she had reoccurring about once to twice a week of dizziness that came out from nowhere. She was immune compromised because she get biologic for her rheumatoid arthritis. Her head just snapped and the room rolled around but she had ongoing about and it just, and she was scared to drive at this point. She have had regular medicine, she take every day. Simvastatin but she do not know how much, she take 2 other pills. In the morning she took, Valsartan/HCTZ and the other one is Levoxyl before her vaccine, she took both of those in the morning before she had the vaccine. Levoxyl is 0.05 milligrams, the Valsartan is 80 milligrams /12.5, the Simvastatin is 20 milligrams she take that at night. Simvastatin from 2000, Levoxyl it was may be 2022 and the Valsartan, it was about 3 years, so say, 2020. Related to treatment she stated, her doctor had not talked to her about it. She had no medicine. She had been trying to see if she eat little food she start to feel fine, that helps that sort of thing.  The information on the batch/lot number for bnt162b2 omi xbb.1.5 has been requested and will be submitted if and when received.