collywobbles

I've a 1999 A3 1.6 petrol, today i reversed out of my parking space drove forward a bit and then BAM! the car stopped and would not move forward, it was stuck. Tried second gear, it was also stuck, then i put it in reverse and it moved. this seemed to free things up and i was able to drive it again. Anyone think they might know what this is? I'm freaking out incase it happens while at speed. Happened a few months ago and i thought it was the brakes, got them checked and they were fine.