Physics glitch?

I was driving an 18,000 pound modified, solar powered, Mechanized Infantry Carrier.

I was in a military seat with a 5-point harness on. I was not overburdened. Every single part on my vehicle was in perfect condition, including the spiked ram attached to the front. (Mechanics 10).

I was travelling at 20mph, and I can only assume I hit an underbrush and physics screwed up, because suddenly I was dead and all my gear took damage. (No zombies in sight, well fed, well rested, no drug usage, multivitamins taken once per day, etc.) I watched deathcam and the vehicle continued to roll, with me in the driver's seat, plowing through a lab and some trees without losing any parts before I exited.

Anybody know what happened?