Dreaming is a normal psychological phenomenon that occurs during a person’s sleep.
Studies have shown that most people dream every night. If one awakens at this stage of dream sleep, one will clearly remember the dream at that time. If one awakens 5 to 10 minutes past the dream sleep stage, one will only remember having dreamed, but cannot recall the specific dream, and if one awakens 10 minutes past the dream sleep stage, most people will think that they did not dream.
In general, most of the nerve cells in the brain are also resting while a person is sleeping, and when a few areas of nerve cells are in an excited state, the person will experience dreams. Some people may have watched some frightening or scary films and videos or novels before going to bed, and these stimuli form part of their memory, leading to nightmares at night.
Sometimes it is also related to sleeping in an inappropriate position, such as sleeping on your stomach or having your hand on your chest pressing on your heart, in which case it is easier to have scary dreams. Nightmares are also associated with many illnesses, such as: depression, neurosis, post-traumatic stress disorder, sleep and breathing related disorders, and stroke.