Gas pedal stuck? 2nd time happening now

[cloudballoon]

My wife has a 2007 Yaris sedan, automatic. 3~4 months ago, I was driving the car and I wanted to pass a slow moving car in front of me on the right lane (and I needed to turn left on the next light anyway), so I got into the left lane and sped up a bit (to ~40mph, from ~30mph) to match the traffic flow speed, then I heard the driver behind me (he was quite far back when I came out from the right lane, I won't consider myself was cutting him off at the time) didn't like that I got in front of him started full throttling and closing in on me. I heard his full-throttling and so I accelerated quickly so he won't hit me. At this time the car when went full throttled, over 6000rpm, all by itself. It continued the high revving and I was soon gonna hit the car in front of me so I drove it to the "left-turn only" lane which is cleared of any car and shifted to neutral. It then quieted down and I can shift it back into D and drive away.

5 days ago, similar thing happened. I was at a T-section and needed to turn right onto a major fast-moving boulevard. I got a small window of opportunity to merge and I took it, but I needed to pick up speed quick to match traffic flow if I don't want the driver behind me (after I merged onto the boulevard) to need to apply break. So I was forceful on the gas pedal (but not full throttling, my car is not drifting/skidding or anything...), but the gas got stuck and revved up to over 6000rpm again. Braking didn't do anything, and again I placed it to Neutral and let it slow down and I was able turn into a residential street and the car slowed to a stand still while the engine is still high revving. I turned off the engine, waited a bit (20 seconds or so) and turned the engine back on, it immediately high-rev back to 6000+ rpm. So I turn it off again, waited like 10 minutes this time and turned it on once again. It got back to normal and I drove back home safely.

I called up my brother-in-law (who's an auto mechanic) relaying what happened, he hadn't heard it happened to a Yaris before and said maybe it's a floor-mat-stucking-the-gas-pedal problem.

I've since removed the floor mat and my wife is driving my car now instead. I'm not using the Yaris much (self-employed work at home guy) -- only twice in the last 5 days -- but want to know what are the possible issues and hope to prevent it... can anyone help me please? Thanks!