I made two trips from SoCal to Atlanta in two weeks. During the 1st trip, I got 10 hours of sleep in 3 nights, and I was so tired because in the days previous to those three, I'd gotten less than 5 hrs a night.
I flew back to SoCal for a few days and then left again for Atlanta.
On the 2nd trip, I got 7 hours of sleep in 4 nights, the last 48 hours with no sleep. On the flight home, I conked. Probably with my mouth hanging open.
I ran on caffiene and adrenalin. I'm not sure I could do it again, but at the time, those proposals were such a big deal, there was no way I was going to not get them done.
During those last 48 hours, I remember thinking, "I can sleep when I get on the plane." And I kept moving. If I had stopped moving, I'm sure I would have fallen asleep standing up. :)