Hello,
Thanks for posting your query.
Motion sickness while on a boat , commonly called sea sickness can occur in some individuals who are more prone to it. It is caused by exposure to complex, passive, and most often three-dimensional movements of the body in different vessels or environments such as cars, busses, trains, ships, airplanes, funfair rides etc which causes disturbance of Perception of movement by body. This results in a condition in which a disagreement exists between visually perceived movement and the vestibular system's( inner ear) sense of movement.
The common symptoms are Dizziness, fatigue, and nausea but in severe cases vomiting, muscle weakness, psychological changes can occur.
It's not clear if you are referring to loss of movement or tingling numbness in hand in your son but in any case if it's as a result of the motion sickness it should have resolved once he is out of the boat . So most probably it's due to either a severe motion sickness or a sideffect of any medication taken( if taken) or due to a pathological cause( nerve damage/ vascular damage etc) .
Hence it's advisable you consult a MD physician or the child's pediatrician for a thorough examination and confirmation of diagnosis.
If due to motion sickness it's reversible and will resolve with treatment .
So please do not worry but do get it investigated by a specialist.
Hope I have answered your query.
I'll be available for any follow up queries.
Regards

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