What's the chance to suffer a heart attack?
It's random, but on average once every 40 hours (real time).
This chance is configurable in the mod settings.

Does the explosion deal damage?
As far as I know, no.

Why did you make this?
This mod adds an exciting new element to the game! You never know when you'll end up exploding, and throughout your gameplay you're constantly reminded of your mortality. (Or you forget all about it and suddenly explode, giving you a heart attack irl too)