Motion sickness is the result of the discrepancy of information your brain gets from the various sensors.
Both with flying and sailing and reading books in moving cars your eyes tell you there is no or little movement and your balance organ in your inner ears tells you there is movement.
This confuses the brain and sickness is the result.
Anxiety and tension make these things worse.
I dont know why the armbands work but those who have used them claim they do. Mind you those who found them useless may be too embarrased to admit to using them.
FD