Last year a coworker and I had been working on a project non-stop (quite literally) for about a week. At this point, she had been up for at least 72 hours straight, if not more.
We were flying DCA-CVG-SFO, and during the connection, she just feel asleep on the floor at the gate. I tried to wake her up at the end of boarding, and she just muttered in her sleep "You go ahead, I'll grab the next flight."
Eventually I got her onboard.