Autistic Child Has Seizure Followed By a Fibrillated Heart.

Hi, I have a very important question. My brother who has autism was brought to the hospital by ambulance this past sunday. My mother over heard him in the bathroom sounding like he was throwing up. When she arrived to check him, he was convulsing and eyes rolling into the back of his head. My father was frantic trying to find out what was going on, when he collapsed in my father's arms, and lost consciousness. My father immediatelly administered cpr, and after a few minutes he started to breathe again, but had no power in his body what so ever. The ambulance arrived and off he went with a "fibrillated heart". He was in the hospital for a few days where they took so many tests of him. Chest xray, blood work, ultra sound of the heart, cat scan and mri's. They found nothing. His heart stayed fibrillated for about two days, before the medication they gave him through the iv started to work. His heart rate is now in the normal 70's thank god, but he still has to take the medication, because they dont know if it is possible it will happen again. After all this testing, we still dont know what happened to my brother, and we are deathly afraid to even go to sleep at night without keeping an eye on him. Can anyone possibly tell me what this may be?? My brother is autisitic and cannot speak, so unfortunately he cant tell us what exactly happened. Can anyone please help me with this topic?? Thank you very much!!!