his eyes (fixed)on the ceiling是独立主格结构做伴随状语.
我们常见的伴随状语逻辑主语都是句子的主语,因此只要考虑主被动就可以选用现在分词或者过去分词.而这个句子得主语是he,这个状语要描述his eyes的状态,因此就要加上逻辑主语,而“眼睛”跟“fix”之间是被动,所以用过去分词.再例如,His mother being late,he has to stay at the hospital to look after her.
His mother being late就是独立主格结构.
而“lost in thought”是 “be lost in” 沉迷于,沉浸于这个固定短语作状语时,省略“be”这类be后面跟动词过去分词的短语都是如此用法,再例如,Caught in the heavy snow,our car can't move any further.这个状语就是be caught in 开头的,意为“被困在”做状语时候,去掉be即可