I can't believe they were laughing about it on the ground afterwards.
I once had a very narrow escape when a road went over a rise and suddenly dead ended at the lip of a steep slope without any signs posted
I stopped a few feet short from going over the edge and the first thing I did was an involuntary laugh. I witnessed the same reaction from another driver whose car overturned, but was uninjured.
It happens when you can't believe your extremely lucky escape