I was thinking about this more over the weekend and had a chat with DH about it. I think if DS thought I was deeply unhappy he would be traumatised by my crying - I think kids do pick up on that, just as I used to pick up on my parents deep unhappiness (which they told me wasn't real, but I could tell it was). But considering DH and I are in a very happy marriage, I'm doing the work I love, and I feel happy with life when I wake up in the morning, and considering that after the rare occasions when I've had a cry, when I tell DS 'Feeling better now, right, let's start again!' I genuinely am feeling fine - not wildly happy that things went so pear-shaped, but not stressed either, and from the look of him, neither is he.
I'm still not sure about the idea of lying to him about whether it's because of his behaviour, even though a few of you are sure that's the right way to go. I really appreciate the perspectives and have been thinking about it quite a bit, but I'm just not sure that it's right...
I mean if there were other factors that had made me cry, of course it would make sense to explain them to him rather than blame him for something else that wasn't his fault. But this was very clearly his fault - and he knew it. So if I said 'No I'm not crying because you did that, I'm crying because I'm tired' I am sure that he'd know I was lying, he'd probably (knowing him) ask me why I was lying, and he'd wonder why what he'd done was so awful that I'd lie about it rather than say 'Yes, I'm crying because I've had enough of you being so rude to me, and I don't like being spoken to like that. Now I need a sit down and a cup of tea and I'll be alright again in a minute once we've both had chance to calm down' If it were an emotionally charged atmosphere at home, eg like you describe PutTheKettleOn I think he'd find it traumatic... But it's not.
The last time DS made me cry was a year ago when he kicked me in the face and knocked out one of my teeth (not deliberately, he was flailing when the gp was trying to examine him and... next thing I knew I was spitting blood - thanks to the gp and my lovely dentist I got the tooth back!). I just think if I'd said 'Oh no, DS, I'm not crying because you kicked me in the face, I'm crying about something that happened at work' (sorry, bit facetious, but ykwim!) I think he would find that more traumatic than just 'Flamin' Nora, you've taken my tooth out you little blighter!' Wouldn't he find it weird to know that he'd had an emotional effect on me but for me to say 'No, it's not you, it's [something I just made up]'??