Cats are creatures of habit and comfort. They don't do well with changes like going to the vet, pet carrier, car ride, moving to another home and having a new person in the house can scare and stress them out. The best thing you can do for your cat is pay attention to the body language. If the cat is aroused or stressed out don't try to pet it or pick up the cat. Give your cat space even if it takes hours for the cat to calm down from being aroused or stressed out.
If you have an affectionate cat talk or sing to him/her.
Cats like to hide under things or go to their condo.
Things that cats do to comfort themselves like leaving their scent around with rubbing their face and marking their paws with the scent and scratching posts area. When you transport your cat in a carrier to unfamiliar places take the items that bears your cat's own scent and that should make your cat very happy.
You can also use Essential Oils honeysuckle or lavender have calming effect on cats. Put a couple of drops on a paper towel just to air the room. Only use a small amount at a time. Essential Oils can be very dangerous to cats if they come in direct contact with them.
For treats with calming effects in them consult with your vet.
Interactive play with a lure toy is important to repeat daily. It's a calming benefit for your cat.
Playing soft classical music or cat-specific music will increase the sense of calm.https://www.youtube.com/watch?v=YUhcY86ybi0
Professional Pet Sitting Services offered in the Upper to Mid-Pinellas County Area