Please - give yourself a break. Are any of your children old enough to leave "in charge" for a short time while you sneak some Mom Time for a walk, bath or nap? Maybe in exchange for a special privilege that the others don't get - that's what my Mom used to do for me when raising 6 kids and working 2 jobs. By the way - instead of trying to take a nap in a house full of kids (with all the scary noises they make trying to be quiet) she would take her car to a nearby park, lay her head back and rest.
Remember, to be your best at work, you need to take care of yourself too. And the kids won't notice little things left undone at home.
Sue