Palpitations; Fatigue; Difficulty breathing/dyspnoea; syncope (fainting from drop in BP); Fever 103°F; Altered sleeping habits; This spontaneous case was reported by a consumer and describes the occurrence of PALPITATIONS (Palpitations), PYREXIA (Fever 103°F), SLEEP DISORDER (Altered sleeping habits), FATIGUE (Fatigue), DYSPNOEA (Difficulty breathing/dyspnoea) and SYNCOPE (syncope (fainting from drop in BP)) in a female patient of an unknown age who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch no. 084J21A) for COVID-19 vaccination.     No Medical History information was reported.    On 07-Feb-2022, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 07-Feb-2022, the patient experienced PALPITATIONS (Palpitations) (seriousness criterion hospitalization), FATIGUE (Fatigue) (seriousness criterion hospitalization) and DYSPNOEA (Difficulty breathing/dyspnoea) (seriousness criterion hospitalization). In February 2022, the patient experienced PYREXIA (Fever 103°F) (seriousness criterion hospitalization), SLEEP DISORDER (Altered sleeping habits) (seriousness criterion hospitalization) and SYNCOPE (syncope (fainting from drop in BP)) (seriousness criterion hospitalization). The patient was hospitalized on 09-Feb-2022 due to DYSPNOEA, FATIGUE, PALPITATIONS, PYREXIA, SLEEP DISORDER and SYNCOPE. The patient was treated with DILTIAZEM HYDROCHLORIDE (CARDIZEM [DILTIAZEM HYDROCHLORIDE]) at an unspecified dose and frequency. At the time of the report, PALPITATIONS (Palpitations), PYREXIA (Fever 103°F), SLEEP DISORDER (Altered sleeping habits), FATIGUE (Fatigue), DYSPNOEA (Difficulty breathing/dyspnoea) and SYNCOPE (syncope (fainting from drop in BP)) was resolving.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Cardiac function test: abnormal (abnormal) Abnormal. On an unknown date, Electrocardiogram: abnormal (abnormal) Abnormal. On an unknown date, Myocardial necrosis marker: abnormal (abnormal) Abnormal.         Patient was not taking any concomitant medication. Patient had no history of COVID positive. No other vaccines received within 1 month prior to Moderna COVID-19 vaccine.  Batch number for second dose was reported as 037C21A.  Patient started having severe symptoms of palpitations, fatigue, difficult breathing the same night she received the booster. Patient also experienced fever, altered sleeping habits and syncope (fainting from drop in BP). Chest pain or chest discomfort was not observed. Patient was hospitalized on 09-FEB-2022. It was reported symptoms lasted for almost two weeks. Not specified which symptoms. It was reported some symptoms improved some are still ongoing. Specifically mentioned fever of 103-degree Fahrenheit, altered sleeping habits, fatigue, palpitations were improved. Patient never had heart problem or similar symptoms like this before receiving the Moderna COVID-19 vaccine. Patient had no history of Myocarditis/Pericarditis.  Company comment: This is a spontaneous case concerning  a female patient of unknown age with no medical history reported, who experienced the unexpected, serious (hospitalization) events of palpitations, dyspnoea and syncope. The events started the same day after the third dose of mRNA-1273 and continued for two weeks, after which they started to improve. Treatment included diltiazem which could be a confounder for syncope. Diagnostic tests such as cardiac function tests, ECG and myocardial necrosis markers are reported as abnormal (not further specified). The benefit-risk relationship of mRNA-1273 COVID 19 Vaccine, is not affected by this report.   Most recent FOLLOW-UP information incorporated above includes: On 18-Feb-2022: Follow up received includes: Event 'feeling bad' added On 22-Feb-2022: Events, lab data and treatment drug was added.; Sender's Comments: This is a spontaneous case concerning  a female patient of unknown age with no medical history reported, who experienced the unexpected, serious (hospitalization) events of palpitations, dyspnoea and syncope. The events started the same day after the third dose of mRNA-1273 and continued for two weeks, after which they started to improve. Treatment included diltiazem which could be a confounder for syncope. Diagnostic tests such as cardiac function tests, ECG and myocardial necrosis markers are reported as abnormal (not further specified). The benefit-risk relationship of mRNA-1273 COVID 19 Vaccine, is not affected by this report.