disclaimer: this is not a detailed examination of your dream nor a professional opinion, im not an expert.
in psychoanalysis, dreams are explored through word association and past experiences of a person which most often than not were traumatic.
since it is impossible for me and you to talk about the dream per se, let me just share my opinion/perspective on the general thought of the matter..
nun may be symbolizing a belief or value system in your personality, perhaps religion or anything of that sort. In the dream a nun cause you to panic or cause to stir some emotions in you and my guess is that something is bothering you right now, something very threatening for your ego (psyche - for the lack of better lay man's word) to handle, hence, it is being repressed in your subconscious..
not to complicate the analysis more further, just try to examine yourself if something you have done may have contradicted to your belief system and if be brought to consciousness may be very threatening to you.. (e.g. very conservative woman who engage im pre-marital *** would develop a strong sense of guilt about it).
DONT TAKE this seriously... unless you talk to a professional.. this is just for my mental masturbation..