Arm hurts; Exhausted; unconscious; Like a seizure; I felt not ok/terrifying; not coherent; I do not remember much; Trouble keeping my eyes open; Trouble supporting my head and my whole body; Profuse sweating; Skin went drastically pale; Pupils went all the way ot the edge of her eyes like there was no color; Vomited; This spontaneous case was reported by a consumer and describes the occurrence of LOSS OF CONSCIOUSNESS (unconscious) and SEIZURE LIKE PHENOMENA (Like a seizure) in a 29-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 037F21A) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.   On 29-Aug-2021 at 3:10 PM, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 29-Aug-2021, the patient experienced LOSS OF CONSCIOUSNESS (unconscious) (seriousness criterion medically significant), SEIZURE LIKE PHENOMENA (Like a seizure) (seriousness criterion medically significant), FEELING ABNORMAL (I felt not ok/terrifying), MEMORY IMPAIRMENT (I do not remember much), OCULAR DISCOMFORT (Trouble keeping my eyes open), DISCOMFORT (Trouble supporting my head and my whole body), HYPERHIDROSIS (Profuse sweating), PALLOR (Skin went drastically pale), MYDRIASIS (Pupils went all the way ot the edge of her eyes like there was no color) and VOMITING (Vomited). 29-Aug-2021, the patient experienced INCOHERENT (not coherent). On an unknown date, the patient experienced PAIN IN EXTREMITY (Arm hurts) and FATIGUE (Exhausted). The patient was treated with SODIUM CHLORIDE (SODIUM CHLORIDE IV) (intravenous) on 29-Aug-2021 at an unspecified dose and frequency and ONDANSETRON (ZOFRAN [ONDANSETRON]) on 29-Aug-2021 at an unspecified dose and frequency. On 29-Aug-2021, LOSS OF CONSCIOUSNESS (unconscious), SEIZURE LIKE PHENOMENA (Like a seizure), FEELING ABNORMAL (I felt not ok/terrifying), INCOHERENT (not coherent), MEMORY IMPAIRMENT (I do not remember much), OCULAR DISCOMFORT (Trouble keeping my eyes open), DISCOMFORT (Trouble supporting my head and my whole body), HYPERHIDROSIS (Profuse sweating), PALLOR (Skin went drastically pale), MYDRIASIS (Pupils went all the way ot the edge of her eyes like there was no color) and VOMITING (Vomited) had resolved. At the time of the report, PAIN IN EXTREMITY (Arm hurts) and FATIGUE (Exhausted) had not resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On 29-Aug-2021, Blood potassium: on low end of normal on low end of normal but still within reference range. On 29-Aug-2021, Blood sodium: on low end of normal on low end of normal but still within reference range.  The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) was unknown.   For mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular), the reporter did not provide any causality assessments.   No concomitant medication provided.  It was reported that patient received blood work including a hematology and chemistry panel which showed her sodium and potassium were on low end of normal but still within reference range. She also received a portable chest x-ray, but did not have information on the findings from that. She was discharged from the emergency room at 5:27 pm approximately 2 hours after arriving.  Company comment: Based on the current available information and temporal association between the use of the product and the start date of the events, a causal relationship cannot be excluded.; Sender's Comments: Based on the current available information and temporal association between the use of the product and the start date of the events, a causal relationship cannot be excluded.