Nightmares can be triggered by many factors, including: Stress or anxiety. Sometimes the ordinary stresses of daily life, such as a problem at home or school, trigger nightmares. A major change, such as a move or the death of a loved one, can have the same effect.
Some people believe that nightmares and dreams have a deeper meaning and that they can symbolize your subconscious emotions. A bad dream about falling means you feel powerless or out of control, or that you are afraid of failing at something. A nightmare about drowning means you feel overwhelmed by your emotions.