back on one's feet从字面上看意思是“重新站起来”，它的真正意思是“病后痊愈，恢复健康”，当然它也有“东山再起，重新振作起来”的意思。

【例句】
You'll soon be back on your feet if you have a good rest.
如果你好好休息你会很快康复。

I still believe that he is bound to be back on his feet despite bankruptcy.
尽管他破产了，我仍然相信他会重新振作起来，东山再起。