It seems to me, that unless your body was *mostly* ready to go into labour anyway, even a bad fall wouldn't put you into labour.
I had a bad fall (onto concrete) when I was about 35 weeks pregnant. I rested for a few hours, because I was contracting alot, with contractions that felt stronger than normal BH. They stopped, though (thank goodness)
The jolt of falling was very possibly what set labour into motion for you. However, had it not been that, maybe it would have been spicy food the next day, or sex, or a long walk, or any number of other things that are attributed to getting labour going.
Have you considered not having your cervix checked prior to labour? How valuable to you was it to know that you'd dialated to 1 cm? How damaging was it to know you hadn't thinned out?
Failing all else, maybe make a visit to somewhere with a trampoline part of your kicking labour into gear plans?
~Teresa, raising DS (Jan. 02) and DD1 (Jun. 04) and DD2 (Dec. 11) with DH.