I've fallen three times in the past month.
Over a dog: On a trail, came upon a couple and their three unleashed dogs. The dogs all came toward me. I passed the first by stepping off the trail into a bush; again on the path I hurdled the second; the third proved to be too much for me and I tripped over it. All this within the span of two seconds. The owners just laugh.
On a trail: steep downhill, uneven ground. Boring fall.
Off a trail: pouring down rain, a six-inch-wide trail on the side of a hill, the trail headed downhill and was also slanted right to left...I was trying to step carefully but I took a wrong step, my leg slid out from under me and I flew for a second then landed on my side in the mud. Didn't hurt, and I looked xhardxcorex for the next 7 miles.
But my worst fall ever was on Hayward Field, a year or two ago. I was doing 600s and was feeling great on one somewhere around #6 or 7. I came around Bowerman Curve with 100 to go and must have kept turning left as it straightened out. I stepped on the curb with my right foot, and at one point the right side of my foot was on the curb and my ankle was on the ground. Went down hard (reflexively hit Stop on my watch before I hit the ground) and yelled DAMMIT, which got looks from the joggers and stadium-runners. Swelled up to grapefruit size and I was out for a week.