Hi B.,
I had the exact same problem with my now 11 year old, beginning when she was almost 5 years old. Your story sounds identical to mine. For the life of me I could not understand how she ended up facing night time fears like that, when I always tried so hard to shelter her and do everything "right"...loving supportive family, all the security it seems like a kid would need...I adamantly kept her from questionable stuff on TV with literally ONE exception when she was 4. I left her with my mother and supposedly when she left the room for a minute, my daughter got the tv remote and changed the channel to something scary...needless to say I was less than thrilled about that. And that's literally all it took to introduce us to the world of nightmares...
I have an idea for you, although this went against the ideal, and my pediatrician didn't even recommend this idea (she didn't reject it, either, it just wasn't the first choice of options...). For us, absolutely NOTHING else worked but this. And it literally took me years to come up with this idea...I soooo wished it had come to mind sooner because we experienced exactly what you are describing for about 3 years until we tried this. I let my little one fall asleep watching a light-hearted dvd cartoon. I know, sounds bad and probably isn't what every kid needs to do, but my daughter needed to redirect her thoughts before she went to sleep, and just could not do it on her own. This was the ONLY way for us that worked. At first I would talk with her, pray with her, read to her and stay with her until she fell asleep, but then I had TWO more little girls during these years so with three little ones to put to bed, it wasn't possible for me or my husband to spend this much time with her every single night. That's where the dvd came in handy, she could focus on it when her thoughts would linger on something scary and it would help her think her way out of them...It literally became a life-saver for us until she just eventually outgrew this phase. And they will outgrow it, it just takes some time. It's a normal part of childhood. Our little girls are just a little more sensitive to this than maybe other kids.
Just thought I'd pass that idea along as a last resort, because it really did help us when nothing else at all worked. I hope your little one (and YOU) get some relief soon. Don't worry, you're not alone.
God bless,
K.