Your subconscious may be dealing with something. Try to take parts of the dream and see if there is any deeper meaning to it. While nightmares are bothersome, if it is a reoccurring dream it may be your body trying to tell you something or your mind trying to settle something it has been struggling with. Anxiety can also play a role. I try to understand what the dream is trying to tell me, so that I can resolve it while I am awake. A few nights ago I had a dream about a possum, which is something I have never thought of before, so I found it odd. After some research I concluded it was someone deceiving/lying to me, which is something I was suspicious of at the time, so for my mind to have that reaction in a dream made sense. It is not to say that the person was deceiving me (which I believe they really are) but because I strongly believe it, my dream manifested as such in the form of a possum.
If you are able to understand why the dream is happening (basically what is on your mind that has been stressing you out or causing anxiety) then you may be able to resolve it while awake, take acknowledgement and the dream may stop. To aid in sleep, you can use lavender oil (I rub it on the bottom of my feet), or try a quick routine meditation prior to bed.