I still sometimes get dizzy from 1/2A planes, even when using 42' lines if they can't do manuvers like loops and horizontal 8s. anything 52' and over is ok.
I did find something that helps from a few ballet dancers. You look ahead of the plane so that it's just inside of your peripheral vision, or maybe slightly ahead of the plane and focus on a fixed point until the plane is passing it. Quickly move your head to a new spot ahead of the plane and repeat. This helped me get over the dizzyness while I was in high school before I could afford anything bigger than an 099 powered plane.
Also, I've found that drinking a reasonable amount of water when flying on a hot sunny summer day also helps.