YOU SAID:

I fell down the upstairs neighbor

INTO JAPANESE

上の階のお隣さんから転落してしまいました

BACK INTO ENGLISH

I fell from my neighbor upstairs

INTO JAPANESE

上の階の隣人から落ちました

BACK INTO ENGLISH

fell from a neighbor upstairs

INTO JAPANESE

上の階の隣人から落ちた

BACK INTO ENGLISH

fell from a neighbor upstairs