I´m sorry thammock
I can understand that it would probably be impossible to select the "one" most shocking moment.
However, I think what they´d do is ask for a moment that stands for many other moments.

Also, to be able to do this sort of therapy, you cannot be suicidal, strongly dissociating or seeing/hearing things that aren´t there.

So it´s not for everyone, if your symptoms are to "dangerous".