On Friday, 12-3-21 I was in an accident in my local Costco parking lot while backing out of my spot. While backing out of the spot slowly with the wheel turned, my 2014 Subaru Forester had a sudden and extreme acceleration in reverse doing a reverse u-turn into a parked car causing considerable damage to the rear end of both cars. I am certain that I did not to press the gas pedal as this is a busy parking lot and I always back out very slowly just covering the brake. There is some kind of mechanical issue with my car that caused this malfunction. I was evaluated by paramedics and taken to the local emergency room with a significant bump on the back right side of my head. My car is currently available for inspection. I am in the process of reporting this to Subaru of America to see if they can inspect/evaluate the car.