@chocolatelog
This then is the nub of the matter, the context for the whole thread that has been missing. You have depression.
That is why you feel so anxious and are so joyless, can't see the benefit of exploration and downtime, struggle with something like filling in forms. That is why you struggle to control your volatile emotions when stressed. You are ill. Why you tried to deny this or dismiss it as just being 'set in your ways' I don't know. It is the missing piece that makes everything else make sense.
I feel very sorry for you, depression can suck all the pleasure out of life for you. I lost my own mother to her depression last summer, so I fully appreciate how severely it can impact on somebody.
However, from the child's perspective, I also know how the weight of a parent's depression can tilt the whole balance of your life and your own mental health.
You owe it to your five children to seek treatment for your depression. You also owe it to them to ensure it impacts on them as little as possible. That is a heavy burden to bear when you have your own wellbeing to manage, and you didn't know when you had them you would become ill. You didn't sign up for this battle or this burden. I'm sorry. But it is still your duty to protect them from your illness, because no-one else can.
Forget this holiday (although again I'd suggest you try and persuade DH to take the older children on his own). Focus on getting your depression under control. It is not easy and it is not a one-size-fits-all solution - you may be helped by medication, counselling, therapy, mindfulness, some combination of all of these. And it may work for a while and then it may stop. Try something else. Keep trying.
Depression is like cancer; it's unfair, and random, and it can be fatal. You must take it seriously and act. You have to fight it like it's a threat to your life, because it is. And you have to treat it like an infectious disease and practice good mental and behavioural 'hygiene' to try and prevent it from infecting the lives of your children, because if you don't they will be fighting the same battles in 5, 10, 20 years' time.
I know what I'm talking about. Please do take this seriously.