The next thing I knew, I was facedown in the water.
1.大家老师说face down是表语，但我觉得face down整体是副词，请问face down的词性到底是什么？若是副词的话我有两种剖析，face down修饰整个句子，去掉该副词后主句是I was in thewater.，第二种是face down修饰介词in，请老师鉴别一下。
2.前面的名词词组The next thing I knew是什么成分？貌似不是左偏置结构，由于The next thing和I根本不是同一个物，也不太可能是句子的同位语，由于若是同位语应该放在后面而不是开头，请问这到底是什么使用方法？
1 face down 本是一个独立主格结构，即face being down省略了系词being。不少名词+副词构成的独立主格结构渐渐演变为副词，被当做副词用。词典已经把face down作为副词网站收录，也可以拼写为face-down。I was face down in the water. 应该剖析为副词face down作表语，in the water为状语。假如句子为I was in the water face down. 则是介词短语作表语，face down作状语。像 He was sitting beside her in the room. 剖析为进行时态+地址状语。He was in the room sitting beside her. 剖析为系表结构+分词作随着状语。
2 先看一下下面句子的剖析：
What is important，you are safe. what is important为评注性状语（传统语法剖析为插入语）。
What is important is that you are safe. what从句为主语从句
You are save, which is important. 关系分句作句子状语（传统语法剖析为which引导非限制性定语从句）。
注意what=the thing which, what is important=the thing which is important，即先行词+定语从句。
你的句子：the next thing I knew 就是一个名词+定语从句，= what I knew next。剖析办法同上：
The next thing I knew, I was face down in the water. 逗号前为评注性状语（插入语），后面为主句。
The next thing I knew was that I was face down in the water. 主系表结构，that从句为表语。
I was face down in the water, which was the next thing I knew. which从句为句子关系分句（传统语法剖析为非限制性定语从句）。
