Nightmares are fearful dreams occurring in REM sleep that result in sudden awakenings in the night, after which it is difficult to fall back asleep. They are therefore associated with some insomnia-type sleep disturbances and can either cause some anxiety or be associated with it. Nightmares are more common in people who have thin boundaries and a higher level of creativity or in cases in which there are psychopathological problems. Pregnant women may have nightmares, often related to the birth of the baby.
Nightmares about negative things – death, cliffs, lost trains or mazes – are probably due to depression.