My worst crash was at all of 3 mph!
This summer, I hit a rut going uphill on my singlespeed at low speed, ran out of momentum, and found myself falling. During the fall, I had that famous sensation of time slowing, during which I was thinking about how this crash was "no big deal".
I somehow fell directly on the end of my bar, which struck to the left of my sternum, just over my heart. I had previously lost the end cap for my ESI chunkies on that side when I clipped a tree gate, and my jersey nearly had a circle of fabric punched out of it. For about 30 seconds, I sincerely thought I was going to have a heart attack by the side of the trail, but I recovered and limped home.
When I got home, I had a yellow and purple bruise the size of a softball over my heart. Damn thing hurt every time I took a truly deep breath for 6 weeks or so.