Hi and welcome to the Chiari forum.
First Chiari is a congenital condition meaning you were born with it, and it is a malformation of the skull.....many that have it may be unaware since we have always had it and do not recognize symptoms as symptoms as we have always had them....they are our "normal"....HOWEVER it is possible to acquire Chiari BUT it is low lying tonsils and not a true Chiari BUT the symptoms are the same as are the treatment options.
You , if you have true Chiari may not have noticed your symptoms, but the continuned falls may have triggered your symptoms to flare/worsen so you noticed them more.
Anyone can develope low lying tonsils and sometimes they retract on their own, while some require surgery.
As for whip lash, it can aggravate Chiari symptoms.....I had whip lash and I know it made my symptoms worse.I am not sure what could be done to help prevent someone from possible injury like this due to the nature of the contact sport...just as in football is dangerous as there are many head and neck injuries that do not show up until years after playing the sport.....
Not sure if that helps, if it has created more questions just keep asking , I'll try to answer the best I can,