Not sheer terror, and entirely self-induced, but there I was...
In a T-34, sightseeing in central California, with a friend in back. 8000 feet or so high and a couple of miles off the Big Sur coast on a gorgeous day. The plane was in the old Navy "yellow terror" bright yellow paint scheme. Looking down down the right wing while doing a steep turn, I couldn't help but notice how picturesque the yellow wing looked against the sparkling Pacific far below. Still looking at the wing, I started marveling how such a surface can interact with the invisible air in such a manner as to allow us to travel through the sky:
"What a miracle! Held aloft by forces we can't see — free to enjoy this astonishing perspective. But what if that's not really how it works? What if it's really faith that holds us in the air? Implausible perhaps, but that would mean that doubt could ruin the miracle. I hope I don't doubt. Oh no, I doubted!"
The resulting flash of panic lasted long enough to make me yank the plane level again before accepting that, no, it probably is that aerodynamic thing after all.