be on one’s back 卧病；卧床不起
A：Where’s Eric? I haven’t seen him for quite a few days.
B：He’s on his back now.
A：I’m sorry to hear that. But he was all right last week.
B：Yeah, he was caught in the rain the other days. He has got a very bad cold.
A：艾力克在哪儿呢？我好几天没见着他了。
B：他卧床不起了。
A：真不愿听到这个。上周他还好好的呢。
B：是啊，那天让雨淋了，他感冒得严重。