on your last legs idiom informal
快累死了;奄奄一息了
A person who is on their last legs is very tired or near to death.
We'd been out walking all day and I was on my last legs when we reached the hotel. 我们出去走了整整一天，到达旅馆时我都快累死了。
It looks as though her grandfather's on his last legs. 她爷爷看起来快不行了。