Nightmares generally occur during the later part of sleep, when REM*phases last longer and dreaming becomes more vivid.

Psychiatrists believe that a nightmare is an intense dramatisation of the significance of problems or anxieties encountered recently in waking life. A sort of over the top replay of a difficult daily problem.

They generally occur, not during the REM phase but in the deep slumber of earlier sleep. The sleeper often awakes suddenly with a loud cry, sitting up terrified, but usually unable to remember the cause.

Certain foods consumed before sleep are said to cause certain types of dreams. Cheese and chocolate are often blamed for night terrors and nightmares.

*rapid eye movement.