Tips that have helped me....
Keep a stack of already made meals in the freezer, if you get out of bed knowing it's going to be one of those days, take out the pre made meal to defrost and reheat at dinner time. The family get a decent meal, you've used up less energy and time spent making dinner from scratch also reduces mummy guilt giving them rubbish cause it's all you've got in you to do :D
let the bulk of the weekly chores you do wait and try cheating instead eg launder only what you and the kids absolutely need, hang on hangers to dry straighter and if something must be ironed either don't wear it or try just ironing the bits you see eg cuffs and collar. clean only what you see or use and ignore everything else, skim vacuum the obvious animal fur, fluff, grit etc and leave a thorough vac for when your energy is back on board.
Let the kids earn extra pocket money or have fun helping you cook but don't worry about how good a job they do, just be content that something less is on your list eg let the kids get all the stuff for their own lunch boxes and you just make the sandwich or supervise them doing it themselves, let the kids strip and remake their own beds, you just do the tricky bits, sweep the floor etc etc
Hope that helps.......JJ