Drove to and back from Calgary to Vegas on two separate occasions last year. 24hour straight drive. First trip by myself and second trip with a company. Was not well rested, took in minimal fluids and ate minimally. I was pretty much alert the whole time, as I do enjoy long commutes, beautiful scenery, winding roads, and singing to my favourite tunes helped me get there 90% of the time. The other 10% I relied on caffeine and a 30 minute nap.
Doing the daily grind driving between work (had to work 2 full time jobs back to back back then) was the most difficult I find. When you're working you don't notice it, but once you stop and make the drive to your next job that's when it hits you hard. On two occasions I had to wind down the window and have wind blow into my face on the highway and couldn't wait to get off the highway. Yeah, it was bad.