This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
The lead actor got sick all of a sudden and we couldn't find another actor to fill in for him. It was such a nightmare.
I had a bad dream that I turned into a fat cat that couldn’t walk.
I heard you can make yourself have nightmares if you sleep with your arms folded across your chest, so I tried it and I had a dream that I was cleaning a toilet nonstop from morning to night.