Synchronized vomiting - now here's a new Olympic sport
Seriously - MJ has it right. It's the cameras. Unless you are used to doing aerial photography (or photography from any moving object for that matter), this is highly disorienting and induces nausea PDQ. Reason being that the motion your body experiences and what your eye sees through the viewfinder or monitor are out of sync. Even worse, btw, from a boat that rocks and sways w/o forward motion. If you take people up again, tell them NOT to take pictures, at least not for a while.