I don't do shifts, but I once flew back in from Spain at 2am, then had to get up at 6am, fly to Amsterdam, then as I was about to leave Amsterdam at 6pm I was told I needed to fly to Naples for an emergency bit of work (a US Senator was coming aboard a yacht, who's main telecommunication system had failed - and they needed it up and running for a video conference meeting the next day). So I flew off to Italy, worked till 4am, slept 2 hours. Then had to fly back to Amsterdam, finish a meeting, then fly home that night at 6pm.
Ok so I did sleep a little bit, but with the travel it didn't half exhaust me.