It's not too difficult to flip a tank in darkness. All it takes is a ditch of some type and hitting it at the right (or extremely wrong) angle. A lot of commanders of flipped tanks die as a result since they are normally operating outside of the hatch with night vision goggles on (which have terrible depth perception).
Tankers train for roll over drills to insure both the commander and loader learn to duck inside and hang on so they don't get crushed. I almost flipped my tank in 1988 during REFORGER. We were traveling down a narrow farm trail and our right track went over the edge.
I immediately ducked inside, but my knuckle headed loader looks to his right doesn't see me there. He starts yelling "The L T Fell Out! The L T fell out!"
I grab him from below and tell him to get his [effing backside] in here. Fortunately our driver was a great and got us back on the road without a tumble down the valley below. My wingman in the tank behind us thought we were goners.