From the information you’ve provided it sounds like your brother had a pulmonary thromboembolism that presented as a seizure. Pulmonary embolism (PE) is a blood clot in the lungs that puts strain on the heart and leads to low oxygen levels in the body. There are several heart conditions in which the first symptom is a neurologic one, and pulmonary embolism is included in this category as a rare cause of seizures (case reports describe patients that are your brother’s age). Physicians speculate that low oxygen supply to the brain is what actually causes the seizure.   It would be difficult to guess the condition of your brother that day, but it sounds like he wasn’t feeling well. The important question is what caused his PE (they typically arise from a clot elsewhere in the body, including the legs, arms, or pelvis) and how can he reduce the likelihood this will happen again.   Though every case is unique, there are many situations in which heart function outlasts breathing when a person is critically ill. Your brother may have stopped breathing because of the PE, or because of the medications needed to sedate him in order to place a tube for breathing. These tubes are typically placed when a person’s own breathing isn’t maintaining the oxygen levels required for the body and heart to function. The best person to answer this question, though, would be the physicians that cared for him in the hospital.