Is the Check Engine light on? There are two thresholds of mis-fire detection. The first, or less serious, will store fault codes for the affected cylinder(s), and light the CEL. In more severe mis-fire events, the engine control unit will shut down the affected cylinder(s) to prevent causing damage to the catalytic converter. Once the key is cycled, the cylinders are all turned on again (until the problem re-occurs). This sounds like case with your car. The shut-off threshold is determined by the frequency of mis-fires per thousand engine revolutions. Checking for fault codes will tell you which cylinder(s) are acting up. Good luck