noun
A frightening dream; used in the same sense as the English word. Common in both literal and figurative contexts.
昨夜はひどいナイトメアを見た。
I had a terrible nightmare last night.
その事故は彼にとってナイトメアだった。
The accident was a nightmare for him.
悪夢 is the native Japanese word for 'nightmare' and is more common in formal or literary contexts. ナイトメア is a direct loanword and often carries a slightly more modern or dramatic nuance.
Borrowed from English 'nightmare'.