Crumbs sorry, I'm at work and almost as soon as I posted I had to go to a meeting. Thanks so much everyone for your responses. A lot of people have asked whether he could have been half-asleep or dreaming. I don't think he was- he seemed wide awake to me. I am 99.9999% sure I didn't hit him- the only reason I can't be 100% sure is because I was dozing a bit at the time and I guess you can't rule out something funny happening. But I've never done anything like that before and I would expect that if I had hit him in my doze then I would have woken myself up, which didn't happen until he responded to me so harshly.
When I denied hitting him, he just kept saying "no, you hit me. You hit me, fact". He was cold and precise in the way he said it. And he wasn't normal to me in the morning. When he got up I was already up and dressed and having breakfast and he just ignored me.
I have to be honest, I would never have said something like "shut up you twat" or the other jokey responses many people say they would have given. I am a bit scared of him if I'm honest with myself. It's not even so much being scared that he would hit me but rather being scared of how he would react. If I say the wrong thing he gets offended and does the shutting down thing.... Others are more cheeky and teasing with him- for example, I'm always really struck by how my sister will be very jokey with him, but it doesn't seem to be a dynamic that he and I are able to have. Perhaps I am too tentative with him- I definitely feel like I tip toe around him, which is very different from the style of relationship I've ever had before and certainly not a relationship model that I grew up with (my parents have a great relationship, 38 years and going strong).
Others have asked about DH's background. He didn't have a violent background but I find his family quite different from mine. My family has plenty of faults but it is very loving and affectionate and pretty rowdy- if someone is upset with someone else, they tend to have a big screaming match where terrible things are said but then you end up crying together and reaffirming how much you love each other. There were three strong women plus my father and there tended to be lots of slammed doors, stalkings off, highly emotional rants etc etc. But it always ended well.
I would describe my sister and I as well brought up with good values and respect for others, but we would also answer back to our parents and be cheeky and probably completely annoying as teenagers. It was all just part of life. DH's family is much quieter and, I find, quite remote in the way they deal with each other. DH's father died about 10 years ago, before I met DH. They seem to have had an odd relationship. DH has massive issues with authority and authority figures (part of the reason he had a falling out with my parents is because he thought they were trying to control us, it was a stupid fight about our wedding which turned into a 5 year rift which I deeply regret). Apparently DH's father would not tolerate anyone disagreeing with him. There were the facts according to DH's father and there was no other way. I don't think he enforced this through violence but it seems to have been the household law. As a result DH left home at 17.
In terms of him shutting down, it happens most times we have a serious disagreement. If I do something wrong, he will close down for hours. It can be a few days. He seems perfectly happy to get into bed, turn his back on me and go to sleep, go to work the next morning. I usually have to expend a lot of energy to bring him around to talk to me.
Finally, I don't know how he feels about me earning so much more than him. He says he is fine with it, happy about it even. He works in an industry where there are a lot of redundancies at the moment and he says that my job takes the pressure off him because, unlike a lot of his colleagues, he is not the sole breadwinner with the whole family looking to him to pay the mortgage. He would never admit to having a problem with it.
It's refreshing, although very frightening for me, to realise that others think this behaviour is weird. I don't think he is abusing steroids, although it's a valid suggestion based on his interests in weights etc. I do wonder whether he's having some sort of breakdown and whether it has been going on for years, certainly since the nose incident. He has a reasonably stressful job and not the best temperament for dealing with it. My job is as stressful, if not more stressful (and I work much longer hours) but I tend to let things wash over me a bit and don't take work too seriously. DH tends to fixate on things that have happened and get quite obsessive about them.
I also genuinely wonder whether he has a psychological condition. When the nose thing happened I did think he had psychological issues and I desperately wanted counselling at that time but DH said that we could sort our own problems out. I don't know why I didn't push this. In many ways I have just been too scared to explore these dark edges of our relationship. I can't talk to anyone in RL about it because I am sure that it would turn them against DH. That leaves me even more isolated, if you see what I mean.
I am just so frightened and unsure as to how to take this forward. I honestly don't believe DH would actually hit me but I am scared there's something fundamentally wrong with him. As I mentioned in my OP, I had to see him in another context mid-morning today(we had to go to the bank together, after having gone our separate ways to work) and I found myself looking at him during the meeting and just wondering what the hell was going on in his head. And wondering how the hell I deal with this. I looked at DD as I was going to work this morning and felt chilling fear that I was not going to be able to offer her the loving and healthily dysfunctional (if you know what I mean) family environment I grew up in. I am sitting here feeling nauseous and fearful. I have a function after work this evening so he will probably make sure he is in bed and asleep (even if he's not) by the time I'm home so I've got another day of this to endure.