[arnon123847]

As far as I experience it, it's not the irresistible desire to jump by itself, but the idea of having an action at hand that would be the last action one would ever take--without having any recourse after it has been taken, and the fear that one might unconsciously or whimsically set into motion that action before being able to analyse it rationally.

It's the same fear as standing on a platform where a high-speed train passes by.

As I see it it's the fear of the small gap between realizing and rationalizing where there's a guarantee that the rationalization will not occur or be futile and irreversible.