And there,almost___in the chair,sat her little brother,who n

And there,almost___in the chair,sat her little brother,who never had to be told to be quiet.
为什么划线处要用lost?lost 不是丢的意思吗?

第6版的牛津高阶上有写：
be lost in sth（1038页）
全神贯注；沉浸于；to be giving all your attention to sth so that you do not notice what is happening around you.
我询问我的老师说可以这样翻译：
在那边坐着她的兄弟,几乎整个身子都陷在椅子里,他是个不用别人说就会保持安静的人.