1997 Blazer, odd acceleration. PLEASE HELP!

I have a 97 Chevrolet Blazer. Today on the Way home from School, the car went "psycho" on me. As i was normaly driving down the road, the car accelerates and decellerates (sp?) without me doing anything. It was as if i was rapidly stomping on and off the gas peddle.

Any ideas as to what happened? How/How much to fix it?

Thanks for all the help!

Is the check engine light on?

Either the engine was loping or you were tapping your foot to the music, your right foot.

As LT said, any engine light's on?

When was the last time a complete tune-up was done?

Was it in auto pilot mode???