Throttle stuck...?

[Strengr]

Not sure if this classifies as a problem, or if anyone has had experience before...

I am driving along, I have 5-spd, and for the sake of argument let's say it's stock. I am jugging along at 3rd and I shift up to 4th, and down goes the accelerator [gently]. I don't really feel anything in the pedal, and the car isn't speeding up any faster, and then all of a sudden, wham, the car kind of jerks forward and continue unabated. Anyway had this happened before?

Note: I wasn't racing, I wasn't doing anything out of the ordinary, just driving alone on the street at 62km/h

TIA,
Strengr