YOU SAID:

I fell down the stairs, and it hurt.

INTO JAPANESE

私は階段から落ちて、それが痛い。

BACK INTO ENGLISH

I fell off the stairs and it hurts.

INTO JAPANESE

階段から落ちて痛い。

BACK INTO ENGLISH

I fall off the stairs and hurt.

INTO JAPANESE

階段から落ちて怪我をしました。

BACK INTO ENGLISH

I fell off the stairs and got hurt.

INTO JAPANESE

私は階段から落ちてけがをした。

BACK INTO ENGLISH

I fell off the stairs and got hurt.