just like people, some dog are more prone to motion sickness. Especially puppies and dogs under a year their , they are more prone to motion sickness because their skulls and internals are still growing.
My pup threw up until he was 6 months old, my friends dog refuses to ride facing foraward and only rides in the car looking out the back window, anothers dog wont get into the back, but insists on have the vent on, and sticking his face in the vent the entire ride (we call him a vent rider)....

sometimes, we just never have answers. it could be that he's more relaxed with a traveling companion and that has eased his anxiety about riding.

when i got pea (146# dane), she had NO clue how to get in and out of a vehicle. we had to LIFT her into the back seat of my truck. when i got home, i had to leave all of the doors open for 30 minutes before she finally figured out how to climb out. it took her a few times to get comfortable with riding but now when she hears the keys jingle, she spins in circles and can't WAIT to go!

I think you may be right.He might have had anxiety about riding in the car, because he threw up for almost two years, and as soon as he had a traveling buddy it stopped. You should have taken a video of your dane trying to figure how to exit the car. Great Danes are the sweetest dogs on earth.

Benadryl can help with this. Ask your vet how much to give. Benadryl has a side effect that stops motion sickness. I've used it myself and it definitely works!

Here is a link that might be useful: The Pet Nanny and Dog Walker

LOL lily, i was so flabbergasted that she didn't know how to do it, i never thought to have the camera handy. she looked SO confused but finally figured it out. hmmm, maybe she was playing me for a fool and just wanted to go for another ride!

yup, i will never be without at least one dane. they are just big ole giant lap dogs, for sure!