The patient has been waking up with anxiety; Felt like indigestion; Left arm pain; waking up in the middle of the night gasping for air; Yesterday the patient blacked out with chest pain/ everything went black; Yesterday the patient blacked out with chest pain; The patient has been having heart palpitations/ the patient has been waking up with palpitations; This spontaneous case was reported by a nurse and describes the occurrence of LOSS OF CONSCIOUSNESS (Yesterday the patient blacked out with chest pain/ everything went black) in a male patient of an unknown age who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.   On 08-Dec-2021, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On an unknown date, the patient received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On an unknown date, received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 08-Dec-2021, the patient experienced PALPITATIONS (The patient has been having heart palpitations/ the patient has been waking up with palpitations). On an unknown date, the patient experienced LOSS OF CONSCIOUSNESS (Yesterday the patient blacked out with chest pain/ everything went black) (seriousness criterion medically significant), CHEST PAIN (Yesterday the patient blacked out with chest pain), ANXIETY (The patient has been waking up with anxiety), ABDOMINAL DISCOMFORT (Felt like indigestion), PAIN IN EXTREMITY (Left arm pain) and DYSPNOEA (waking up in the middle of the night gasping for air). At the time of the report, LOSS OF CONSCIOUSNESS (Yesterday the patient blacked out with chest pain/ everything went black) and CHEST PAIN (Yesterday the patient blacked out with chest pain) had resolved, PALPITATIONS (The patient has been having heart palpitations/ the patient has been waking up with palpitations) and ANXIETY (The patient has been waking up with anxiety) had not resolved and ABDOMINAL DISCOMFORT (Felt like indigestion), PAIN IN EXTREMITY (Left arm pain) and DYSPNOEA (waking up in the middle of the night gasping for air) outcome was unknown.        For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   Concomitant product use was not provided by the reporter.  On 12-Jan-2022, the patient rushed to the hospital. The patient was blacked out with chest pain and everything was normal when he was check out.  The patient had been waking up with palpitations and anxiety and gasping for air. The patient's symptoms are the same but way worse.  The patient was waking up in the middle of the night gasping for air, had blurriness and brain fog.  The reporter thought patient was having a heart attack. Everything went black.  No treatment information was provided.  This case was identified as part of a retrospective clean-up activity where certain emails received in the Moderna mailbox were missed to be booked-in.  Company Comment:  This is a spontaneous case, reported by a nurse, concerning a male patient of an unknown age with no medical history reported, who experienced the unexpected serious (medically significant) event of Loss of consciousness, reported as blacked out, in the context of the booster/third dose of mRNA-1273 vaccine. Latency cannot be properly assessed since the event onset date was not provided. Patient had received 2-dose primary series of mRNA-1273 vaccine on unknown dates, prior to third mRNA-1273 vaccination. The patient also experienced chest pain, heart palpitation, gasping of air upon waking up, anxiety, indigestion-like feeling, and left arm pain. Patient was sent to the hospital, however it was not reported if the patient was admitted or stayed in the hospital for more than 24 hours. No further details about the clinical course, diagnostic procedures and treatments were provided. It was reported that the event Loss of consciousness had resolved. The benefit-risk relationship of mRNA-1273 is not affected by this report.; Sender's Comments: This is a spontaneous case, reported by a nurse, concerning a male patient of an unknown age with no medical history reported, who experienced the unexpected serious (medically significant) event of Loss of consciousness, reported as blacked out, in the context of the booster/third dose of mRNA-1273 vaccine. Latency cannot be properly assessed since the event onset date was not provided. Patient had received 2-dose primary series of mRNA-1273 vaccine on unknown dates, prior to third mRNA-1273 vaccination. The patient also experienced chest pain, heart palpitation, gasping of air upon waking up, anxiety, indigestion-like feeling, and left arm pain. Patient was sent to the hospital, however it was not reported if the patient was admitted or stayed in the hospital for more than 24 hours. No further details about the clinical course, diagnostic procedures and treatments were provided. It was reported that the event Loss of consciousness had resolved. The benefit-risk relationship of mRNA-1273 is not affected by this report.