Kakoneirophobia (from kak meaning "bad, evil", oneiro meaning "dream", and phobos meaning "fear") is an irrational fear of nightmares. This phobia is powerful and it is quite common. It is often connected with oneirophobia, although kakoneirophobia is the fear of bad dreams only, while oneirophobia can mean fear of good dreams as well.
The runaway most common trigger of kakoneirophobia is of course nightmares. It is most commonly suffered by young children. To prevent nightmares, people should avoid thinking about bad things and events while avoiding watching films that portray bad things and bad events, especially horror and disaster films.