Outer Limits 4x4 Board

I have a 1985 Bundera LX 2.4 petrol. So here I am driving down the road and change from 3rd to 4th and I hear a big clunking sound, I lose a considerable amount of power and the car just keeps revving higher and higher. I pulled over and turn it off and it sounded like the engine was trying start, so engine shaking and making sounds aswell, this lasted at least 5 seconds. I left it parked on the side of the road as im too uncomfortable to drive it home.

What has happened to my bundera?!