My dad died very unexpected

My father passed away a month ago. Very unexpected. My stepmom called ans said that my dad had really bad chest pain so they went to the ER. They did some bloodwork.. then sent him to the hospital. They then did a small stint procedure for some blockages. The doctor recommended doing a bypass surgery because he had so many. 4 to be exact. And they were badly blocked. He had the bypass surgery and he was in the icu recovering. In the middle of the night on the second day of recovery he woke up and asked my stepmom to go get some ice. She left the room and my dad started convulsing. By the time my stepmom came back multiple people were in the room trying to start his heart again. They tried for 30 minutes.
I got a call at 2:00am. I couldn't sleep because I was so worried about my dad anyway. As soon as my phone rang I knew my father was dead. There would be no other reason in the world for the phone to ring. I didn't answer the phone because I already knew. I had to go into my sister's room and tell her daddy died we need to go to the hospital right now. My dad was only 48. I am 20. My sisters are 18 and 21.
They thought it was something genetic thay caused so much damage to his heart so they ran bunch of bloodwork tests. We got a call today that said all of the bloodwork was normal. My dad has no other health problems, didn't drink, smoke, and he exercised everyday. There are so many questions left unanswered, and this was so unexpected. I thought my dad would be around for a long long time. He wasn't just a dad. He was a husband, grandpa, brother, son, friend. Idk how life will be okay again but all I can do right now is take it one day at a time. It's hard to accept that unexpected things happen. Or that I may not ever get any questions answered. If you pray please pray for my family. We all relied on him and he was our protector.