I think my scariest moment was when I was about 18 (around 1995/1996). My dad bought an old Farmall C with the tricycle-style front wheel to use out on our place in the country. That thing was a pain. It's electric start had been converted from 6V to 12V and the new starter had enough torque to strip the teeth on the flywheel, thus turning it back to a crank-start. Another wonderful feature was that the PTO was connected directly to the rear axle....
So one day I'm riding the Farmall running the brush hog while my dad is tending a burning brush pile. All of a sudden the front tricycle wheel completely disappears into either a collapsed gopher mound or large ant bed. The drop threw me hard against the steering wheel and I instinctively slammed my foot down on the clutch. Unfortunately the brush hog was still running at full speed and the momentum of that drove the rear wheels forward. My brain was in high gear and time was moving in slow motion. Just when I thought the front wheel was going to sheer off the whole tractor lurched as the wheel popped up out of the hole and the tractor did a wheelie. The front end slammed back down and bounced four or five times before my foot found the brake and the momentum from the shredder ran out. All of that happened in about 15 or 20 seconds.
And of course a tractor that old didn't have a seat belt so the whole time I was primarily concentrating on trying to stay in the seat. Had a nasty steering-wheel shaped bruise on my chest. Doctor said I was lucky I didn't crack a rib.
We finally got rid of that tractor when it got to where it would accumulate water in the gas tank overnight. Nearly broke my wrist twice crank starting it.
The first time I drove our little Mitsubishi BD2G Dozer over a small ridge and the front end pivoted down rather suddenly was a bit of an "Oh Crap!" moment. Of course, I'm used to that now so I don't even flinch anymore.... Unless, of course, I happen to be backing when it happens and I'm not expecting it.