It is truly an amazing day in my life, because thanks to you all, I've found some "answers" for my problem that is exactly the same like yours with similar symptoms. My flashes started 2 years ago, one night to the other and they haven't gone since but with the help of sleeping pills and antidepressants.
My flashes came with pain, not only with the lightning looking flash and bang. Exactly before I fall asleep. And again when I reach the upper state of R.E.M. My dreams are vivid also, down to the smallest details, like being in a parallel world. They are becoming more intense as the days go by, so much-, that I firmly believe I have opened a gate to something, I'm not meant to see. I need help!
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