"刚刚忙完躺下"的英文表达可以是 "just finished up and lay down"。

这个表达方式来自于英语中常用的动词短语 "finish up"，意思是 "完成，结束"。例如：

I need to finish up this report before the deadpne. (我需要在截止日期前完成这份报告。)
Can you help me finish up the dishes? (你能帮我把盘子洗完吗？)

"躺下"的英文表达是 "lay down"。这个动词的意思是 "躺，平躺"。例如：

I'm so tired, I just want to lay down and take a nap. (我太累了，我只想躺下小睡一会儿。)
The baby is crying, I need to lay him down for a nap. (婴儿在哭，我需要让他躺下小睡一会儿。)