When you are frightened in a dream, chances are that you may have been involved in an incident or trauma that relates with your past. This could be related with trauma-related flashbacks, post-traumatic stress disorder (PTSD) or intense fear attacks.
The other cause is one where somebody else was tormenting you in your dream. Dreams can be interpreted as a projection of one’s subconscious mind, which has the most powerful power and will even manifest thoughts and fears into reality.
Being frightened in a dream can signify that a person is afraid of something or unsure about something they are faced with. For example, if you are dreaming of a nightmare where you are in danger, it could be because you have unfinished personal business that needs your attention.