People have nightmares as a spontaneous aspect of dreaming that can release pent-up emotions and be vital to mental health. Nightmares may be caused by insignificant events, such as having a late-night snack, which increases metabolism and brain activity. Nightmares can sometimes be the result of sleep deprivation. Withdrawal from alcohol or drugs, depression, prescription medications and a variety of psychological disorders can also trigger nightmares.
For many people, common feelings, such as anxiety or a fear of anticipated events, can cause nightmares. As with enjoyable dreams, events that occur in nightmares are typically symbolic. For instance, a nightmare in which the dreamer is chased by a racing car should not be taken at face value. Instead, the car may symbolize a feeling of being out of control or overwhelmed by a life circumstance. Nightmares reflect subconscious feelings and do not typically represent future events. A recurring nightmare may take place after the dreamer has experienced a traumatic event, or it may be symbolic of a life predicament that needs to be addressed.
Common nightmares include falling, being chased, experiencing car trouble, being inappropriately dressed in public and feeling lost or trapped. Nightmares are most likely to occur in the early morning hours during rapid eye movement sleep, known as REM sleep, when dreaming usually occurs.