One of the things that can help for me in a bad nightmare cycle is when I wake up, I work at changing the narrative of the dreams.
So, for example, I just had a nightmare about drowning. For this dream, I can kind of make it like a movie. I create a montage of me learning to swim and all the things I have done since I learned to swim. I even added Rocky music to it. And I ended with remembering that the reason I had the nightmare is because I spent the day at the pool yesterday. I was with good friends and my husband and I am a capable adult who has wonderful, safe people in my life.