YOU SAID:

I can’t believe, My head is unterwater.

INTO JAPANESE

私は信じられない、私の頭は水面ではない。

BACK INTO ENGLISH

I can't believe it, my head is not on the surface of the water.

INTO JAPANESE

信じられません、私の頭は水面にありません。

BACK INTO ENGLISH

I can't believe it, my head is not on the surface of the water.