Family holidays can be a lot. Stepping out for a short walk alone is allowed.

A long day with a lot of people in it is genuinely demanding, whatever your feelings about any of them. Noise, questions, old patterns in a small kitchen, and nowhere to be alone: the load is real, and it is not evidence that you love anybody less. Most people assume they have to stay in the room until the whole thing is over.

You can step out for ten minutes. Round the block, to the shop, to the car for nothing in particular. Say you are getting some air, which nobody ever queries, and come back easier to be around.