HEART ARRHYTHMIA; CARDIAC ARREST; SWOLLEN BRAIN; LACK OF OXYGEN; SHORT-TERM MEMORY LOSS; COMPROMISED MOTOR SKILLS; COMA; SEIZURES; LETHARGY; This spontaneous report received from a consumer concerned a 59 year old male. The patient's weight, height, and medical history were not reported. The subject was a veteran and retired. The patient received covid-19 vaccine ad26.cov2.s (suspension for injection, intramuscular, batch number: Unknown) dose was not reported, administered on 24-MAR-2021 for prevention of symptomatic sar-cov-2 virus infection. No concomitant medications were reported.  On 24-MAR-2021, the patient felt lethargic that night, and went to bed early. On 26-MAR-2021, he had seizures. On 29-MAR-2021, patient was admitted in the intensive care unit (ICU) after driving and slumped over due to a coma. Doctors noted that he had heart arrhythmia and cardiac arrest. He had foam coming out the mouth. On 29-MAR-2021, X-ray were done that showed no blockage and no heart attack. The patient was intubated. Doctors also noted a swollen brain due to a lack of oxygen.  On 03-APR-2021, the patient woke up from his coma and was out of ICU. The patient long-term memory (things that happen 5-10 years ago and earlier) was fine, but his short-term memory had been compromised. For example, he was unable to remember his name. He was unable to complete normal motor skills like walking and dressing. At the time of this report, patient was in rehab. He had a heart defibrillator placed in his body. His wife emphasized that he did not have any pre-existing conditions.  The action taken with covid-19 vaccine ad26.cov2.s was not applicable. The patient recovered from coma, cardiac arrest, and lack of oxygen on 03-APR-2021, had not recovered from short-term memory loss, and compromised motor skills, and the outcome of lethargy, seizures, heart arrhythmia and swollen brain was not reported. This report was serious (Hospitalization Caused / Prolonged, and Other Medically Important Condition).; Sender's Comments: V0: A 59-year-old male patient with no pre-existing medical conditions felt lethargic the night after vaccine and went to bed early. Two days after vaccine he had seizures (details not reported.) Five days after vaccine, the patient was admitted to the intensive care unit (ICU) after slumping over while driving with "foam coming out" of his mouth. Doctors noted that he had heart arrhythmia and cardiac arrest. "X-rays" were done that showed no blockage and no heart attack. The patient was intubated. Doctors also noted brain swelling due to a lack of oxygen. 10 days after vaccine, the patient woke up from his coma and was out of ICU. The patient's long-term memory (things that happen 5-10 years ago and earlier) was intact, but his short-term memory had been compromised. He was unable to complete normal motor skills like walking and dressing. An internal cardiac defibrillator was placed. At the time of this report, patient was in rehab and recovering. The lethargy is likely related to vaccine. It is possible that the subject experienced new onset seizure disorder, although a direct causal association to vaccine cannot be established based on the information provided. It is unlikely that the cardiac arrhythmia, subsequent cardiac arrest, or resulting anoxic event were related to vaccine, without a plausible mechanism.