Trying to be healthy is bad for my health

Went to Sourland Mountain with DS's scout pack. Contrary to the brochure, the easy level Pond Trail was too difficult for me. After giving a jump to a nice, athletic-looking couple, they told me to stick to the parking lot based on my (lack of) ability on a bike. So while in the lot, a car comes speeding in. I squeeze the back brake and start skidding on the loose gravel. BAM! I twist my knee, which was in horrible shape to begin with. So I pack up and go back to the car and knit til the boys get back. Hopefully I'll be ok tomorrow so I can go out on my new bike and enjoy the gorgeous day.