N3

たとたんに

The instant or moment, As soon as, Just as

乗っのっ

た

とたん

に

落馬らくば

する

。

Fall off the horse right after mounting it.

と同時に

At the same time as, The instant, The moment, As well as

なり

As soon as, The moment, When

たちまち

Immediately, Quickly, Suddenly, In a moment or flash

が早いか

As soon as, No sooner than, The instant that, No sooner had

直ちに

At once, Immediately, As soon as