Very dangerous to do my man. Exhaust fumes can come up through the floor of the vehicle and kill you in your sleep. ..fuck that , i had a 50 hours stint once, i tried to drive, i started to see shit like another car on the highway, i would hit my brake like a mofo only to see there wasn't any car to start with, and alot of other shit, i just stopped at a gas station and took a nap i woke up about 7 hours later with my engine still running.