Could be similar to the first drop moment, except this time you didn't drop your bike. This time you - avoided - the incident and possibly bought a lottery ticket afterwards.
My biggest "oh shit" moment came on a 4 or 6 lane downhill stretch coming back from Osoyoos. The road was wide, farms on both sides with perfect visibility in all directions. The downhill is my excuse for a very long braking distance that came later.
There was a truck parked on the right side of the street with 4-way flashers on. As I came close the truck made a sharp right turn to a field across the highway. red alert, eyes wide the brakes were hammered. The crossing truck suddenly looked like a train crossing the street starting long ago with no end. I stopped before reaching the truck but I'll be damned if it wasn't the biggest "oh shit" moment I've ever had.