Does your horse ‘explode’ all of a sudden?

I often get the question what to do when a horse all of a sudden ‘explodes’. Before the explosion it seemed as if everything was under control, but then you get a burst of tension that you didn’t expect and it felt like it came out of nothing.

It’s a very unpleasant situation, because how can you prepare yourself and your horse for a situation that you don’t feel coming?