Hi welcome to HCM
I can understand your concern for your son's feeling of anxiety.
Dear Actually, when one part of your balance-sensing system  senses that your body is moving, but the other parts don't. For example, if you are in the  moving vehicle , your 
inner ear may sense the motion of waves, but your eyes don't see any movement , you get 
motion sickness .
 Nausea, 
vomiting, 
dizziness, sweating, and a sense of feeling unwell are the normal symptoms of Motion sickness , which is very unpleasant ,
Meclizine prescribed by your dr  is an antihistamine that is used to prevent and treat nausea, vomiting, and dizziness caused by motion sickness. It may also be used to reduce dizziness and loss of balance (
vertigo) caused by inner ear problems.
 If you feel any unusual symptom on taking this medication, as its unwanted side effects  , report to your dr immidiatly .
You can take 
Homeopathic  Cocculus 30 /4 drops in a cup of water /Take 2 table spoons as 1 dose out of this mixture  / every 3 hour / before  starting journey .
It is a tested and treid formula 
Hope this helps solve your query  Take car . All the best