So I know I'm super late to the motion sickness discussion, but I had a crazy experience the second time I rode Cosmic Rewind that I had to share.
My group got to ride in late October, the 21st. We got a lightening lane for the AM, and loved the ride so much we decided we wanted to try again for a boarding group in the afternoon. We were successful, and were surprised at how quickly we moved through the queue. When we were finally boarded, we noticed the train was stopped, and nothing was happening. We looked back, and there was a group of four people from the DAS line fighting with a group of cast members. There was an older, heavyset woman in a ECV who wanted to ride the coaster. She was at least 70 years old, and at least 275 pounds. The cast members were trying to warn her that due to the intensity of the ride, and the motion sickness effects, they highly discourage her from getting on. Nana wasn't having it, and insisted that she was fit to ride. This was going on for at least 5/10 minutes. The cast members eventually resigned that if the party could get her into the coaster, she could ride. They plopped her in the last row of the ride, and we were off!
Our party was a little nervous at first, but the second the coaster reverse launched, it was over. Nana had her arms in the air, smiling ear to ear, screaming, laughing, and singing along with Blondie. It was the best ride experience of our entire stay.
I understand that motion sickness effects every person differently, but to those nervous about the effects of this ride, I absolutely think it's worth the try!