YOU SAID:

I have never fallen down from a horse

INTO JAPANESE

私は決して馬から落ちています。

BACK INTO ENGLISH

I never fell from the horse.

INTO JAPANESE

決して馬から落ちた

BACK INTO ENGLISH

Never fell off his horse

INTO JAPANESE

彼は馬から落ちたことはないです。

BACK INTO ENGLISH

Not that he fell from the horse.

INTO JAPANESE

彼は馬から落ちた。

BACK INTO ENGLISH

He fell off the horse.

INTO JAPANESE

彼は馬から落ちた。

BACK INTO ENGLISH

He fell off the horse.