I know doctors work really long shifts like that, but as a CNA, you're not allowed to work a 24 hour shift. Not only is it a bad idea as far as your employer is concerned, it's also very hazardous -- not only to your health, but also to the health of everyone you're responsible for taking care of. You will be fatigued, you will make mistakes, you will not remember things as well, and your feet will absolutely kill. I've pulled 16 hour shifts, and by hour 14, I'm feeling every minute after that: in my feet, my ankles, my back, my eyes, my thoughts, and I'm usually starving and starting to feel irritable. 12 hour shifts are no big deal, once you're used to them. Don't over-do it. If you work too much as a CNA/RN/LPN/anything related to patient care, the burn out will do more harm than anything else -- and the car won't be worth it. TL;DR - take care of yourself when you have to take care of others. Best of luck to you.