In Fairy Tail, Natsu is prone to getting sick whilst on modern transport. I am asking this question because it kind of annoys me when he gets motion sickness while fighting someone on board train or other forms of transport. These are the known forms of transport that he gets sick on such as...
... And many and all forms of transport that moves.
I think an exception to his motion sickness is when he is flying on Happy, but can't really think of anything else that he doesn't get motion sickness on.
- And waves, just discovered in Episode 133 (quite strange).
Generally, he gets motion sickness from all non organic transportation. He also gets motion sickness when riding on other people. He is also known to get sick from looking or thinking about all different forms of transport, e.g. looking or thinking about trains.
Was it ever explained in the anime or manga why Natsu suffered from motion sickness? And why did Wendy's motion sickness spell not work at all? Did something happen to Natsu in his life that made him suffer from motion sickness? If yes, please include it in the answer! Also, please refrain from using the reason "Natsu built up immunity to Wendy's motion sickness spell" in your answer, unless that's all you can possibly give me.
Answers are kindly appreciated.