Death from a heart attack or suicide?

My friend's son died early Sunday morning. He was only 20 years old and had no physical problems other than he was bipolar and had severe ADHD. He was on medication for these. They did an autopsy and are doing toxicology tests to find out, for sure, what killed him. They won't know the results for several weeks, right now they are uming it was a mive heart attack. Is there any symptoms he would have had that we should look for in either situation? It was very sudden, he got up around 4 am and ran to the bathroom appearing as though he was going to be sick. When he didn't come out after a few minutes, his little sister got her mom and when she went in he was already dead.