You need to decide if your pet is ill and needs medical attention or if your dog or cat is just a bit “put out” after having been on a plane. They are not used to plane travel and so it is quite normal for them to be a bit miffed for 24-48 hours after their flights. Any doubts go and see a local vet. That is always the safest option. Pet travel by air is very safe, but there are some recognised but rare consequences which definitely do need to be acted upon – older pets can become dehydrated, large breeds of dogs can develop bloat/twisted stomach as a result of the air changes within their stomachs – both of these require veterinary attention and to use your common sense to decide if they need medical attention of not.