I've driven some insane miles in one trip, including the Tucson to Amarillo run in one stretch of about 11 hours plus some chasing time. This was when I was younger and did not have money for a motel. I've also chased some hurricanes where I was up for over 48 hours. Any longer than that and you do begin to lose your mind. One thing I've noticed is that some people are more prone to falling asleep while driving than others. My three best friends were killed years ago when the driver fell asleep and rolled the vehicle. I had traveled with the driver before and I knew he had a habit of falling asleep, so I backed out the fatal trip at the last moment. I keep a pillow and blanket in my chase truck now days so if I find myself exhausted, I pull over somewhere safe and sleep. It's also important to keep an eye on the driver if you are a passenger.