lie on one's back~

lie on one's back~
lie on one's back~lie on your back 是仰躺着,直白翻译是躺在你的背上.
那请问lie on one'S back 中的one's 可以替换成 his her my Tom's
变成lie on my back.lie on his back .lie on her back.lie on Tom's back.
难道是躺在我的背上.躺在他的背上?
lie on Tom'S back 到底是应该是 躺在汤姆的背上，还是汤姆仰躺着。