How do I set boundaries?

My department is REALLY short staffed. I’ve maxed out help from other departments and stores. I work 12.5-13.5 hr shifts 5 days a week and work through my lunches. I understand that the department needs me but I’m only human and I’m burned out. I cry during every shift and hope I get into a car accident on my way home so I’ll have a “legit excuse” to take time off.