It is embarrassing for everyone when someone gets airsick. We have all felt, at least a little, of that uncomfortable feeling . Most pilots when they start their flying get a little queasy. Many just quit flying because they do not know or their instructor did not tell them, queasiness is not unusual.
Many pilots do get airsick when they start flight training, but usually it goes away.
But there are many people who give up too soon. It seems that there are a number of factors why people become air sick, but most do, thankfully, get over it eventually . As an operator of an FBO for over 20 years and a CFI for over 25 years I have tried to let people know that it is not unusual and the queasy feeling will go away with knowledge and practice. I have found the most effective method is to assure the passenger and to teach them what is going to happen and how safe this is. Knowledge does help to alleviate some of the fears.