A nightmare's a dream which causes a strong unpleasant emotional response from the sleeper, typically fear or horror, being in situations of extreme danger, or the sensations of pain, bad events, falling, drowning or death. Such dreams can be related to physical causes such as a high fever, turned faced down on a pillow during sleep (most often in the case of drowning nightmares), or psychological ones such as psychological trauma or stress in the sleeper's life, or can have no apparent cause.… (More on Nightmare)