Any idea what would cause a person to have a feeling that they were going to "black out" on a non-looping roller coaster (I actually felt that I couldn't see for a couple seconds, but didn't feel like I'd passed out--hard to explain)? My son and I both had the same sensation on the new Italian Job Turbo Coaster at Kings Dominion recently at launch. It was bumpy at the beginning--no loops, but very fast.
I have low blood pressure and figured that along with the fast launch lowered my blood pressure even more, creating the strange feeling. I don't know if my son also has low blood pressure or not. We went on it again later, but he was fine that time. I was better, but still dizzy.
BTW, I will go on pretty much any type of coaster and the only type I don't like/can't handle are the real rough/jerky coasters because they cause migraines, so I am no ride chicken by any means. Any my son (12yo) will ride any coaster. Oh, and according to my 18yo DD, when she was at Kings Dominion earlier in the week, she had the same feeling.