nightmare

noun

• A demon or monster, thought to plague people while they slept and cause a feeling of suffocation and terror during sleep.
• Sleep paralysis.
• A very bad or frightening dream.

  "I had a nightmare that I tried to run but could neither move nor breathe."

• Any bad, miserable, difficult or terrifying situation or experience that arouses anxiety, terror, agony or great displeasure.

  "Cleaning up after identity theft can be a nightmare of phone calls and letters."