2005 Vauxhall Astra acceleratoe pedal moved

I drove off to find that my acc. pedal was not there. I pulled up and found that it had folded in two and tucked itself up out of the way. I yanked it and unfolded it and it drove OK. I am concerned that this will happen again whilst I am driving. I am nort aware that any warning lights lit up. Any advice out there on why, how this happened and what i can do to make sure it doesn't happen again?