Answer :
Answer: The "X" person is the zombie
Explanation:
In the description, we were told that zombies always lie thinking it's a true statement and human always say the truth, and they are sure in true.
In general we now know one mostly Make true statement, and one make false statement thinking is true.
The two person being questioned already knows that one of them is crazy. X said we both are crazy, which is a false statement, because we are certain that one of them is crazy, though here he thinks he is right. And Y said "at least one of us is stable", which is a true statement, because we know one of them is meant to be crazy.