Bumper jacks and cars don't get along has been my personal experiences I was working on one of my old cars years ago using two bumper jacks to raise and lower the car while I worked on it on a paved asphalt driveway, I was lowering the front end and the bumper jacks started to lean to the right side and dump the car on top of my 3 yr. daughter who was palying along side the car, luckily she wasn't hurt at all, the front tires where not on the car yet and it fell so she was in between the front spindle and the outside of the fender, I thought I had killed her, that scared my to my wits ends. Thank God I didn't I never let any kids play around any cars I was working on after that. I'm hoping your injurys are not serious or permenment I'm sure you where using a floor jack and not bumper jacks as I have had the same problems with my Harbor Freight floor jacks. I don't use bumper jacks anymore either.