Q: Wobbling, veering at freeway speed

I recently got in a car accident. I was traveling at about 75mph when all the sudden my car was wobbling and started to veer to the right, when I tried to correct it was like it over corrected to the left and by the time I righted myself I had traveled through two lanes and had slowed to about 45mph as I hit (mostly brushed) against a cement barrier. I put on my hazards and got off the freeway staying at about 30-35mph at which point the car didn't seem to wobble even half as bad. I'm wondering what could've caused this? I took the car into the dealer and they are being a bit difficult and of course are saying that any damage was most likely due to my accident. However, body damage isn't that bad and they won't give me answers as to what could've caused something like that before an accident.

My car has 100000 miles.
My car has an automatic transmission.