Well, not sure if it's really sickness. He doesn't throw up, but maybe he's nausea's. All I know is that he trembles, pants, and seems very concerned and nervous. Poor little guy travels with my husband 5 hours on Mondays and Fridays, and is miserable every trip. His "sister" travel partner is fine as are all the rest of our clan. Any suggestions to calm him down. I don't want to tranquilize him. We tried the Thunder Suit, but he is in between sizes and it didn't work.