Posting to answer the original posters question all these years later. It is known that Mr Candy had family history of heart attack and he also smoked and was overweight. What I read in Joe Eszterhas’ biography back in the day was just how much John drank and smoked.
Joe Eszterhas was for a time a seriously popular script writer and known drinker and drug taker but he met his match with John Candy in this paraphrase from his book (page 628) - “Hollywood Animal” detailing his meeting with John Candy when John Candy was negotiating the possibility of filming a script Eszterhas had written.
Essentially Eszterhas was going by John Candy’s office and was surprised when he found out that John’s office was an actual bar with tables, jukebox, barstools etc and John was conducting the meeting behind the bar the entire time.
Again Eszterhas was always bragging how messed up he was getting in Hollywood but he bowed down to the king on that day.
Candy chain-smoked the entire time - a cigarette was never out of his hands and at one time had 2 going and was smoking both at the same time.
Eszterhas had 5 beers while at Candy’s “office” at the same time Candy drank 13 rum and cokes!
Later that night they went out to dinner and Candy had 8 ore rum and cokes!
Another friend of Candy’s remembered doing publicity in Monte Carlo with Candy and when Candy didn’t return to LA the next day as planned the friend eventually caught up with him via phone - still in Monte Carlo - still partying.
John Candy was a lovely man - said by everyone who ever met him - but it would appear he may have had some demons that he was trying to quell as well.
He is missed.