As someone who has experienced both, it is the sudden unexpected movements that cause motion sickness. And if I am tired, my mind cannot coordinate between the

As someone who has experienced both, it is the sudden unexpected movements that cause motion sickness. And if I am tired, my mind cannot coordinate between the movement I see to the movement I feel. And now I realize that in the first case, it is a personality issue where if I am stubborn/stiff/unyielding, I will get annoyed at unexpected movements. I find this to be true also with my wife :D