nightmare

a frightening dream that you have when you are asleep

pesadilla, mal sueño

Collocations have a nightmare

• I had a terrible nightmare last night.

  Tuve una pesadilla horrible anoche.

a situation that is very difficult or unpleasant and seems impossible to deal with

problema, dificultad

Collocations nightmare of

• The traffic is a nightmare.

  El tráfico es un problema terrible.