If you're tired, you'll sleep. I remember a few years ago ona bus tour I fell asleep standing up leaning against my luggage in a hotel lobby because some village idiot forgot to book the room for the bus driver. I got a room that nite, after sleeping for nearly an hour on my feet. Another time I had to sleep in the lobby on a sofa because I had no hotel room. I've slept in rigs and busses on up hill and down hill grades. When I'm tired, I'm sleeping.
One thing I will NOT do is sleep on an exit ramp.
People are trying to slow down! hello?
I'll park on an entrance ramp, where they're tryin' to gain speed...
much safer in my opinion.