What causes travel sickness?
The exact mechanisms which cause travel sickness are not fully understood. What we do know is that a combination of uncontrolled travel and stress or anxiety can produce very strong feelings of nausea and cause vomiting. Humans and dogs manage to balance thanks to a clever mechanism contained in the inner ear which sends signals to the brain. The movement caused by being in a car or at sea stimulates this mechanism which then bombards the brain with signals. These signals are made worse by stress (perhaps caused by previous bad experiences) and stimulate areas of the brain which cause nausea and then vomiting.
Only when the movement stops will the nausea slowly subside as the brain activity returns to normal.
Travel sickness drugs work by blocking the signals in the brain which cause vomiting. Some of these also cause temporary drowsiness or sedation because of their effects on other parts of the brain. However, not all travel sickness pills have these effects – ask at your vet surgery for more information on different treatments.