Ricardo:
It's been a long time since I've taken a bus, but I've flown many times without a problem. The only time I was airsick was my first flight, which was on a DC 3 and I walked the length of the plane while it was flying.
Do you think someone's likely to have bus sickness problems if they're okay when they fly?
I don't think you would but then again, I have sickness for cars, buses, planes but not boats. I haven't ridden a bus for about 35 years! I hope I don't have to again either. My bus memories are filled with smoke and body odor. I hope it's a lot better now. I do have good memories of where my mom and I went on the bus though. 