A man walked in off the street and fell flat on his face, unconscious.

一个男人从街上走进来，脸朝下摔倒在地上，昏了过去。

《柯林斯英汉双解大词典》

He fell flat on his face.

他脸朝下地倒下。

youdao

So the Londoner stood up to leave and fell flat on his face.

于是伦敦人起身离开，却直挺挺地摔倒在地上。

youdao

He started to fall again, caught himself, froze in a hunched-over position, hurtled forward, fell flat on his face, chucked his chin on a root.

NEWYORKER: Tenth of December

The game ended in comical fashion when Hooper rounded goalkeeper Pernis but stubbed his toe and fell flat on his face as he tried to score seconds before having another effort chalked off after a questionable offside decision.

BBC: Sport - Football - Dundee United 1-3 Celtic