I'm not sure I should be posting this on here. Even though I seem to be quite open about things despite being identifiable in RL I actually don't share much in the way of details.
But I think I need to share and get some input and this is probably the best place for it. Brace yourself, it's a bit long.
DS (as many of our children do) operates from a higher anxiety base than most children, his "norm" is what others would probably consider to be anxious in their children though he has learnt to cover it up better over time. So we live life on a spectrum from slightly anxious to full on phobia, OCD handwashing and hyper-vigilance. It peaked a couple of summers ago and hasn't been as bad since but it does fluctuate up and down.
DS's sleeping has deteriorated recently (last month or so, I can;t pinpoint exactly) - he's not usually a great sleeper though that's possibly because he just doesn't need as much as other children. But have regressed back to not being able to get to sleep easily (calling out repetitively "night mum") and waking two or three times a night and getting in with me at around midnight/1am. He's also more "tactile" during the day - needs to hold on to me when we sit down, and has been holding hands with me a bit more (had previously considered himself too grown-up!).
So last night he got out of bed at about 10pm and came downstairs to see me (he never does this, he just shouts to me so he can hear that I'm there) looking visibly distressed and was unable to talk. Just stood looking at me. So we played 20 questions and I eventually managed to get out of him what the problem was.
He is having "dreams" (I think it may have started as a dream but may be now him just thinking about it in bed) that everyone he loves/knows has died in a disaster leaving just him on his own. The only people left on earth are people who hate him. 
I felt/still feel totally inadequate and terrified of cocking it up.
I said it was good to talk about these fears and that I could imagine that would be a very scary thought and it would scare me even as an adult. We talked about how its OK to be scared by your thoughts but that you needed to understand how likely they were to happen and to think about the difference between things that were real and were fears inside your head. I compared the "real" things to be scared of as being crossing the road and riding your bike and how you can help yourself by learning to do it safely etc.
I explained that thoughts inside your head still belonged to you and though it might not seem like it, you could influence them. I said it was like being the director of a film and that you could decide you didn;t like the plot or the characters and you could choose to do other things to make the film better - like planning a bunker under the house or giving all your "gang" diamond armour like minecraft (OK probably not the best analogy but I was thinking on the hoof) about how films might be dramatic but they always ended well and that he could choose to change his thoughts to something better but that he was probably going to have to practice that.
I said the alternative was to just acknowledge his thoughts then move on to something real that made him feel happy like our recent holiday.
I also decided to tell him why I thought he had thoughts like this which I'm still not sure was a good idea. I said when he was very small until he was 1, he changed where he lived and who looked after him about every three months. And that though as adults we would understand that those people and places hadn't really disappeared and that they were just looking after different children that it probably felt to a small child like they had all disappeared and that whilst babies brains weren't organised enough to remember it properly which would make it easier to discuss and get through that they did remember the feelings they had at that time and that probably why he was "remembering" that feeling.
I have no idea whether this approach is OK or whether it will help and I'm really unsure whether talking to him about why he might have these fears is a bit too deep.
I feel like I'm floundering a bit. I have a consultation with the EP and DS's teacher on 3rd Feb so will mention this to her as part of his anxiety issues but I doubt she'll have time at that point to get into it much.
So what's the verdict? Should I continue on this road or try a differnt tack, should I bring him back into my bed at night and give up any pretence of him going into his own bed or agree with him that he should go to bed in his bed - perhaps with a nightlight and get into mine when he wakes up.
Sorry thats so long, I've tried to paraphrase - it was a long conversation (and a long night!)