Hi Conan,
I am sorry you are struggling with this. This experience sounds frightening.
I believe talking to your psychologist would be best. This sounds like it may be associated with PTSD in some way. Have you had any traumatic experiences in your past that you could be dreaming about?
This could also be associated with anything you watch/read about possible. For instance, if you play/watch/read a lot of violent movies, games or books, you may experience fear when you go to sleep. Try adjusting the content you view and see if this helps as well.
For some people, caffeine, sugar and other ingredients can influence how you feel/how your sleep is affected. Some people need to eliminate sugar and other additives from their diet completely to benefit and even if someone cuts back when they take in sugar to two or three hours before sleeping, the person can still be affected.
How much time did you try these techniques either in combination or individually? It can take our bodies a couple of weeks or more to adjust to changes either in timing we go to sleep, what we are eating and other things.
I suggest you try going to bed and waking up at around the same time for a month along with not drinking or eating anything sugary, greasy or caffeinated in anyway. I know that doing this really helps me sleep well. Also having a consistent routine at night helps too. I take about half an hour to forty-five minutes to get ready for bed so that I have time to organize things for the next day, relax and this helps my body know that it is almost time to sleep.
Definitely speak with your doctor for more suggestions particularly in relation to getting nightmares.
Take care and I hope I've helped in some way.
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