I couldn't find definitive stats for deaths per year on the toilet. People are probably overdosing and having strokes and heart attacks on the crapper all the time, but the official cause of death rarely includes the location, so who's to know? What I do know is that, when the world ends, the shitter will be your tomb.
Very few apocalypses (henceforth apocalii) result in a peaceful and pastoral sort of setting wherein you just have a lot more time alone to enjoy nature. Most result in madness, chaos, and studded leather. Plus facial hair that never gets to a length ladies find gross.
"Those with spotty growth were the first to be eaten."
Odds are that most of your future diet in the apocalypse is going to be pretty rancid. If you recall, Mad Max was sharing old dog food with his cattle dog. You're going to have maybe a week or two of bliss with cans of soup and Entemann's, and then the shit is hitting the fan. The fresh food will all be spoiled, the good cans will all be gone, and you'll be trying to maintain a healthy lifestyle of running in a mad panic from zombies and robots while full of raw ramen noodles and walnut paste.
That hot dysentery is going to be so steamy and uncomfortable. And eventually it's going to come right in the middle of a running-for-your-life session, and no matter how fast you think you can run while expelling expired butter chicken sauce and pickled egg shits down your thighs, it's not going to be fast enough.
They're called the runs for a goddamn reason.