Had the same thing happen in my wife's car. I installed some new floor mats during the nighttime while the car was garaged, so the floor of the car was mostly dark. Later on I fired up the car and it was immediately on its way to redlining. Of course, completely forgetting about the mats, I over-thought it and checked out stuff related to the engine. Finally got around to checking the mats once I remembered and sure enough the lip of the mat was covering the gas pedal just enough. I was a bit ashamed with myself for that one...
Had a similar situation in my 75 international scout 2 years back. Throttle cable frayed and when I stomped on it the frayed portion went thru the fire wall and wouldn't let the peddle release. Couple seconds later I yanked on the peddle and was able to pull it back thru. Just happy it wasn't anything that accelerated quickly. Still a good scare though.