As with a poster above, worst experience ever was on a Military flight rather than civil.

We were flying on a C-130 from Bagram Airbase to FOB Salerno in northern Afghanistan. For much of the flight, the aircraft flies through the valleys, rather than over the mountains (Himalayas are too high for a C-130).

At one point in the flight, I guess the pilot thought he spotted ground fire coming at us, so he started popping flares and doing "Tactical" flying. This meant that he was bucking and flopping the C-130 as hard as he could. I managed to grab my helmet as it floated up in front of me, and watched my bag fly down towards the tail of the aircraft.

I managed to keep my lunch down, but only barely.