It appeared the man either had a heart attack or a seizure.
The individual who may have saved his life, if he survived, would have been a nurse/emt type individual who was actually on the yellow train at the same time as the guy. She was behind the row we were in. Our row was directly behind the row which the gentleman was in.
He seemed fine on the platform, just standing there right before loading. He was wearing a red hat, which he took off right before boarding, and then started to strap in. As my family and I started to get strapped in, the individual next to him, started yelling for help(they appeared to not be related, and the gentleman looked as if he was riding by himself). The nurse/emt rushed up, after getting her restraints off, and immediately looked at the guy. She was the one who started cpr, and worked on the guy before other KI individuals were able to.
With there being no AED units on site, they waited until the paramedics got there, who used the shock unit on him. I have no idea if the gentleman made it, as he was looking blue even before the paramedics arrived, as he started to look blue before we were barely out of our seats. My 10 and 12 year old daughters were a bit taken back, and we attempted to talk about other things, as things progressed. At that time, the gentleman's wife came running onto the loading platform, and they let her in with her daughter, by opening the gate. We assisted his son over the closed gate, so his family could be together. His wife was obviously visibly shaken, but kept her cool around her kids, by telling them to stay with her, and not watch what was happening. Quite the experience.