Amazing how many sites come up when you google "nightmares and final exam".

Found this idea to stop repetitive bad dreams.
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The raw emotions of repetitive, intrusive nightmares can be "tamed" by a simple, easily learned technique called Imagery Rehearsal Therapy (IRT). If you have multiple recurring nightmares, select just one for the IRT process and use the process every night until the nightmare has been resolved; when that nightmare has been resolved, repeat the process for other nightmares.

1.Write out the text of the nightmare. Tell the story, no matter how frightening, in as much detail as you can remember.
 
2. Create a new ending for the nightmare story and write it out. Be careful, however, to make the new ending peaceful. Remember that the nightmare is grounded in emotions such as raw anger that have been provoked by a trauma. The point of a new ending is to "tame" the emotions, not merely vent them in violence and revenge.