I've been doing Aikido for about 1 year and 6 months and I often (but not always) get dizzy from doing the rolls. Especially the backward rolls. One guy in my dojo suggested that I might not be drinking enough water before class. I don't know if that's it or not. Maybe I hold my breath while doing rolls. Not sure. If there is anyone out there who knows a real answer to this trivia, I'd definitly be interested in hearing it too!