Nightmares can have physical causes such as sleeping in an uncomfortable or awkward position, having a fever, or psychological causes such as stress, anxiety, and as a side effect of various drugs. Eating before going to sleep, which triggers an increase in the bodys metabolism and brain activity, is a potential stimulus for nightmares. Recurrent nightmares may require medical help, as they can interfere with sleeping patterns and cause insomnia. (source : wikipedia)