Cholesterol - the Silent Killer

Hey I figured it out. It was the onion rings!

Early in the show Tony commented about how he hadn't had any vegetables in over a week. His diet on the run coupled with the stress he was under mean that he probably had a massive heart attack and "blacked out" or died there at the end. That's what the fade to black was and it was that final deep fried onion ring that he ate in one bite that put him over the top.

Hey - I'm just kidding but my explanation sounds rational compared to some of the theories making the rounds on the Internets.