2003 S80 Unusal Braking Problem

The evening of 7/19/2003, I just backed out of a parking space at the grocery store, was driving slowly through the parking lot when I tapped the brakes for an upcoming stop sign. It was as though the engine started racing simultaneously and there was barely any brake response. That scared me witless as I tried to tap the brakes again and was getting little response but it felt as though the engine wanted to surge. I shouted my concern to my husband that the brakes weren't responding. He yelled to "turn off the engine." I did this, and the car convulsed to a stop. When I turned on the engine again, there didn't seem to be a problem and we tested the car in a clear area of the parking lot (without any cars or obstacles) before proceeding home. My husband thought that I might have been applying my foot to both the brakes and the gas at the same time. I'm 56 years old, and I've never done that before. When we got home, a few miles from the grocery store, and encountered no more problems, I looked at the brakes and gas pedals and (now the car is turned off in the driveway) I placed my right foot on the brake and gas pedals and my small foot could hardly span the two pedals easily. I think I would have known if I was doing that, but I guess it's possible.
I'll call the dealership tomorrow to get it in (it just turned 40,000), and we had taken it on a round trip from Houston to Chicago to go to a wedding a couple weeks ago (no problems) and it had been in for usual maintenance recently before our trip.
Wouldn't indicator lights come on if there was a problem? We were in such a panic that I don't think either of us looked for indicator lights, but nothing came on during our short trip home from the grocery store.
Any ideas, I'm afraid to take it out tomorrow in morning rush hour traffic to the dealership? Thanks!
Holly