AsapScience has uploaded a really wonderful video about Lucid Dreaming on YouTube. If you are having trouble with nightmares, especially the same, repeated nightmare, I highly recommend this video.
Repetitive nightmares can be really disruptive to not only your sleep, but your life. Nightmares or night terrors are very common for people struggling with trauma or PTSD. They can not only disrupt your sleep, but cause you to develop anxiety about even going to sleep for fear of having night terrors. Lucid dreaming is a powerful tool for taking control over this debilitating symptom of trauma. Check out this very useful video on YouTube, The Science of Lucid Dreaming.