He lay on the bed,with his eyes fixed on the ceiling and fal

He lay on the bed,with his eyes fixed on the ceiling and falling deep into thought
他躺在床上,眼睛盯着天花板,陷入了沉思.
with是做什么的?怎么跑句首去了啊?
and起什么作用?可否换成其他的词啊?
fall为什么用动名词形式?
deep改成deeply行吗?
into起什么作用啊?