Flying in a high sided balloon basket is not like standing in a roof or a high ladder. You don’t get that vertigo feeling. It is more like the ground is unfolding beneath you and because you are moving with the wind, there is no wind blowing. The basket does not rock or sway so you can’t possibly fall out.
You will not get airsick: The turbulence which usually causes motion sickness is completely absent in a balloon ride, as the balloon proceeds with the airflow. The flight of a balloon is almost too smooth to describe.