We use this expression to describe a terrible situation.
You can use this phrase in ………… language.
Spoken
Written
Informal
Example 1
A: Just ten minutes before the interview I got stuck in a traffic jam!
B: What a nightmare!
Example 2
A: I was kilometers from the city, with no petrol, there were no cars, and it was getting dark.
B: What a nightmare! What did you do?