I（主）
imagined（谓）
he had trouble getting himself back together by the time I got back because he knew that I wouldn't laugh.（宾语从句）
he（宾语从句主语）
had trouble getting himself back together（宾语从句谓语：不好拆开了）
by the time I got back(宾语从句中的时间状语）
because he knew that I wouldn't laugh（宾语从句中的原因状语从句）.
that I wouldn't laugh（宾语从句中的原因状语从句中的宾语从句）
真的很复杂
我猜想到我回来的时候他很难让自己恢复,因为他知道我不会笑.