I worked in the first aid department of a Six Flags park. It was not uncommon for people to black out on rides. Many of the rides subject the body to greater G forces and spin you all over the place sometimes causing temporary blood loss in the brain. It's the reason why jet fighter pilots wear shock trousers to direct blood to the brain when they are pulling high G rolls or other maneuvers. If they didn't, they'd pass out while performing combat tactics. Fighter pilots train for this and are, of course, exposed to far greater G forces than we are, but that explains why those of us who go on a coaster once a year that drops you 20 stories then loops you 9 times sometimes get a little woozy or to the point of blacking out while riding.