@EvBGJ I'm sorry to hear that. Christmas is so hard because there are so many stereotypical standards that make comparison very easy and it can feel frustrating and depressing when things go wrong because it seems like so much worse if everyone else is having a great one, plus all the usual support services you would depend on are having a 2 week break, with normal services only catching up around mid January.
In terms of boundaries, is there any way to keep demand low, and remember that they can be re-established after Christmas? Obviously that won't work if it is putting people at risk, but some battles might not be worth the fight right now, especially if you are not on full form and your OH is down in the dumps too.
Is there any way you could decide that boxing day is a whack on the TV day, eat crisps and chocolate all day kind of day, unlimited screen time day, outside at the park for several hours with a cup of coffee day or even an emergency visit to the cinema, soft play or grandma day?
The incessant screaming is enough to drive you bananas. It's the one thing that is guaranteed to reduce any empathy I have for my child to a smouldering pile of ashes, and until someone has experienced a kid genuinely screaming and crying for hours on end, they can't possibly imagine what a toll it takes on an otherwise sane, patient and chilled person. If you have any, ear plugs like loops can help reduce the stress, but in ear ear buds work just as well, or bog standard ear plugs too. Also screaming outside means less acoustic echo (and fewer neighbors listening in lol) so another vote for a walk if you can manage it.
I also found imagining they were a baby and acting according helps a bit- literally picking them up, cuddling them, throwing them in the air, doing baby noises can help. Unmet needs and all that. Give them sensations of bodily security wherever possible. Can you reduce sensory overload, turn off Christmas lights, normal PJs, normal foods etc?
In terms of feeling low, is there any way you can elevate any experiences to make it seem a bit better? It could be anything, taking a box of quality street to a necessary park visit, sneaking some unholy mulled wine and lemsip concoction on a walk to look at Christmas lights, putting on music at full blast over the screaming, speaking with your family on the phone, meeting up with a friend for a brew tomorrow, snuggling up on the sofa to watch crap on TV as they are on their tablet.
Whatever you have to do to make it through the next few days is worth it. You are in the festive trenches because all support is out the window, and you feel alone, which is really hard. Do what you have to do to make it through as gently as you can, then pick up the pieces in the new year is my strongest advice. Be as kind and gentle to yourself as you can, make life as easy for yourself as possible and try to take care of yourself and the OH.
I'm so sorry it's hard. It can feel relentless, especially when you are under the weather.