User blog comment:Godisme/The Flame's Voice/@comment-2214433-20130920205017/@comment-7418318-20130921094607

Only on vehicles. When Happy is carrying him he has no problems with even the wildest mid-air stunts or even being droped and caught again.

So it's either something psychological or the tiny, barely perceptible vibrations rather than the curves, acceleration and deceleration.

That's why I think using his own magic for rapid movements won't trigger his motion sickness.