DD11 was a terrible sleeper from birth and all the things we tried sound a lot like all the things you tried. So I am hugely sympathetic and know how hard this is. I also understand how unsympathetic other people can be. So I hope you take my suggestion in the spirit of that sympathy and not as judgement.
Children often love things that are not good for them (sugar!) or that may not be good for them at a certain time in their life. We do very little sheltering or censoring of DD in any way... except when we see an obvious correlation between something she's doing and some unpleasant result. That's why she's not allowed to watch Disney TV anymore. Because there was a direct correlation between the amount she watched and how bratty and smartmouthed she would then be.
Recently she had a huge anxiety attack in the night. She was fearful because she was reading a ghost story before bed and after the lights went out her imagination ran away with her and she panicked. The story was fine in the daytime, but became too much after dark. And it didn't help that she'd been staying up very late several nights reading and then waking up cranky.
The next night I didn't let her read after a certain time and insisted on lights out. She slept good and woke up happy. And we talked a bit about how sometimes we need to do the thing that's less fun (like not reading and going to bed early) to make ourselves happier... that what we want is not always what's best for us or what will actually make us happy in the end.
If you believe the source of the night fears are the scary topics he learns during the day, then I would firmly restrict and redirect those interests to other areas for now. I suggest going cold turkey for a while -- no vampires, no toxins, no news in front of the kids. No scary shows or books or even game play. Stick to flowers and puppies and stories of kindness for a while (even if you all start to get cavities). See if it makes a difference.
This may help you decide if the anxiety is source specific or more generalized, which could help you make treatment decisions down the road. It also focuses the effort and attention on the day time and not in the night (when emotions run high and no one is feeling rational or happy). It also seems like asking him to change his reading for a while is something he can actually do. Whereas asking a child not to be afraid isn't really a fair request.
It could even be that you couple the change in mental source material with additional night nurturing. So he has to quit researching ebola (bummer!), but he gets to put a sleeping bag next to mom and dad's bed for a while.
