could it be that ur engine had electrically turned off? Sometiems I will turn the ignition off while driving just for shits and giggles. What happens is u have complete loss of power and ur tach will go to zero. Then when u switch the ignition to on the car will pop start itself and keep going. There is no earthly way ur engine could have hit 0rpm while driving in gear. The wheels would keep it going, but if ur electrical system shut it down then ur tach would go limp and ur engine would behave the way u described. Everytime I give my car some gas when i turn it off on the road it will try to drive but give off only .01% of its power LOL.