The "dream argument" is the postulation that the act of dreaming provides preliminary evidence that the senses we trust to distinguish reality from illusion should not be fully trusted, and therefore any state that is dependent on our senses should at the very least be carefully examined and rigorously tested to determine if it is in fact "reality."
In the East, this type of argument is well known as "Zhuangzi dreamed he was a butterfly" introduced by Zhuangzi. It relates that one night Zhuangzi dreamed that he was a carefree butterfly flying happily. After he woke up, he wondered how he could determine whether he was Zhuangzi who had just finished dreaming he was a butterfly, or a butterfly who had just started dreaming he was Zhuangzi. This was a metaphor for what he referred to as a "great dream."

from Wikipedia.