Caller clarifies part of this event is feeling sick to her stomach.; Diagnosed as having a severe allergic reaction to the Covid shot; She didn't feel good, which is not unusual for her when she gets a Covid shot; Felt hot and clammy; Felt dizzy; Knot on her head; Head hurts; Felt hot and clammy; She woke up on the floor, and had actually passed out.; Off label use; Booster; This is a spontaneous report received from contactable reporter(s) (Consumer or other non HCP). The reporter is the patient.  A 74-year-old female patient received BNT162b2 (BNT162B2), on 05Apr2022 as dose 4 (booster), single (Lot number: FM0698) at the age of 74 years, in right arm (right upper arm) for covid-19 immunisation. The patient's relevant medical history included: "blood thinner" (ongoing), notes: Therapy start: Caller states about 3 years ago. Concomitant medication(s) included: XARELTO oral taken for anticoagulant therapy. Vaccination history included: BNT162b2 (Dose 1, Lot number: EL3248, Anatomical location: Left arm), administration date: 06Feb2021, when the patient was 73-year-old, for COVID-19 immunization, reaction(s): "She didn't feel good, which is not unusual for her when she gets a Covid shot"; BNT162b2 (Dose 2, Lot number: EN6202, Anatomical location: Left arm), administration date: 26Feb2021, when the patient was 73-year-old, for COVID-19 immunization, reaction(s): "She didn't feel good, which is not unusual for her when she gets a Covid shot"; BNT162b2 (Dose 3, Lot number: FC3184), administration date: 28Sep2021, when the patient was 73-year-old, for COVID-19 immunization, reaction(s): "She didn't feel good, which is not unusual for her when she gets a Covid shot". No additional vaccines were administered on same date of the Pfizer Suspect. The patient did not receive any other vaccinations within four weeks prior to the first administration date of the suspect vaccine. The following information was reported: IMMUNISATION (hospitalization, medically significant) with onset 05Apr2022, outcome "unknown", described as "Booster"; OFF LABEL USE (hospitalization, medically significant) with onset 05Apr2022, outcome "unknown"; DIZZINESS (hospitalization) with onset 06Apr2022, outcome "recovered with sequelae" (07Apr2022), described as "Felt dizzy"; FEELING HOT (hospitalization), COLD SWEAT (hospitalization) all with onset 06Apr2022, outcome "recovered" (07Apr2022) and all described as "Felt hot and clammy"; HEADACHE (hospitalization) with onset 06Apr2022, outcome "recovering", described as "Head hurts"; MASS (hospitalization) with onset 06Apr2022, outcome "not recovered", described as "Knot on her head"; MALAISE (hospitalization) with onset 06Apr2022, outcome "recovered with sequelae", described as "She didn't feel good, which is not unusual for her when she gets a Covid shot"; LOSS OF CONSCIOUSNESS (hospitalization, medically significant) with onset 06Apr2022, outcome "recovered with sequelae" (06Apr2022), described as "She woke up on the floor, and had actually passed out."; HYPERSENSITIVITY (hospitalization) with onset 07Apr2022, outcome "recovering", described as "Diagnosed as having a severe allergic reaction to the Covid shot"; NAUSEA (hospitalization), outcome "unknown", described as "Caller clarifies part of this event is feeling sick to her stomach.". The patient was hospitalized for off label use, immunisation, loss of consciousness, hypersensitivity, feeling hot, dizziness, mass, headache, cold sweat, nausea (start date: 07Apr2022, discharge date: 08Apr2022, hospitalization duration: 1 day(s)); for malaise (start date: 07Apr2021, discharge date: 08Apr2021, hospitalization duration: 1 day(s)). The events "she woke up on the floor, and had actually passed out.", "diagnosed as having a severe allergic reaction to the covid shot", "she didn't feel good, which is not unusual for her when she gets a covid shot", "felt hot and clammy", "felt dizzy", "knot on her head", "head hurts" and "caller clarifies part of this event is feeling sick to her stomach." required emergency room visit. The patient underwent the following laboratory tests and procedures: Computerised tomogram: Unknown results; X-ray: Unknown results. The caller stated that last week she got her second, Pfizer COVID booster shot. The following day, after the vaccine, she didn't feel good, which was not unusual for her when she gets a COVID shot. She clarified that part of this event was feeling sick to her stomach. She felt hot and clammy. She felt dizzy. She woke up on the floor and had actually passed out. She developed a knot on her head, and later reports that her head hurt. The caller clarifies that it was recommended to go to the emergency room the next morning because she was on a blood thinner. She was on Xarelto. Due to her issues, she was admitted to the hospital. She was diagnosed as having a severe allergic reaction to the COVID shot. She had a CT scan and X-rays. She would be following up on 19Apr2022.  No follow-up attempts are possible. No further information is expected.; Sender's Comments: Linked Report(s) : US-PFIZER INC-202200573710 Same patient and drug, different event separated in time