Why would my dog's behavior in the car change suddenly?

Amy,I've had dogs all of my life and I am an adult and there is one thing that I do know as far as dogs being in cars,they have to have a window cracked at all times so they can stick their noses out,I have read that it has something to do with their equilibrium and ears,I don't know if you have had the windows rolled up in the car,but if you have you may want to try this and see if this could be your dogs problem,I hope this helps you out.