Do anything to excess and it'll kill you, dont take care of yourself and it'll kill you, sit for to long and it will kill you wich is the most likely in this case because he could have gotten a blood clot in one of his leggs and when it got up it came loose and traveled up to his heart or to his brain. This was something that came up within the last two years after someone died on a global flight if I remember correctly but I havent heard much more about it since this time last year. I really dont think that its a sign of the impending doom but it is a clarifying fact that spending to much time sitting wether it be watching tv or playing on the net and not getting up and getting some exercise.