Anything you want, as long as it happened/almost happened/you saw it happen/you made it happen - that sort of thing. You can change the names if you're squeamish, even your own. You can write about what it did to affect you, or what it would have done to affect everyone if it did happen.
It's pretty much a catch-all, but to those who have a little trouble getting started with an idea, it will give you something to go on.
I almost hung myself - very close to not being here. These words would be just ........................................ - nothing much there. Cool. I may treat it as a 'what would have happened to my family' thing.
We'll use this thread as a progress and a panic room. Let's try this - any panic, go advanced and type in red.