Definitely had my seatbelt on. I've learnt, from the car screaming at me, to put my seatbelt on. Sorry car. I won't do it again. This definitely had acceleration from the pressing of the pedal.were you on a slope? I parked car switched off got out then decided to park a bit better. got back in & started. put car in d & it went backwards. found out later that drive doesn't engage if drivers safety belt not on! So car kept rolling backwards - in my panic I think I also must have taken handbrake off with switch.