I suffer from a long term chronic pain. It makes just general life absolutely exhausting. Living with a constant level of pain is exhausting. I don't lie down because I fancy a break, I'd much rather be participating in family life.
I lie down because my mind can't force my body to go on any longer. I feel constantly guilty for not being able to be the kind of parent/employee I could be if I was at 100% capacity. I feel like I'm constantly failing everyone.
I try really hard to make sure DH's life isn't affected by it. I tend to sacrifice work over home because I'm replaceable at work but not at home.
Sometimes I find out DH is in fact doing more at work than he actually needs to - he could do a school run or take a day off with a sick child allowing me to go to work, but he chooses to prioritise appearing completely dependable and going above and beyond at work. His work is known to offer flexibility and family-life balance, he chooses not to take it.
The difference here is I do the vast majority of the kids and he goes to work because I have lots or flexibility and work part-time, but he is full time and career building.
I do resent him when I find out he's prioritising being the ideal employee, because he's basically prioritising himself. But it's a long-term repeated choice to put that first and leave me to struggle.
I get that you're exhausted and need a break too. With kids that young and work everyone needs a break, it is absolutely exhausting in and of itself.
Honestly I think it's OK to do as you're proposing - you're working and looking after the kids. But I don't think it's going to fix your problem long-term. You need to find a bit more available space for yourself somehow or you will burn out and it sounds like everyone depends on you, so that's not an option.
If you're going to do it, then don't waste it feeling guilty.