I used to feel a little dizzy during unusual attitudes as well. Before your flight, have a light lunch and have something to drink (preferably water). When you're in the aircraft, try to stay focused on the outside world and enjoy the experience. Spins are great fun, especially when you remember your instructor is there to make certain nothing goes pear-shaped. If that doesn't work for you, don't fret. You'll get used to the feeling soon enough. I know I did!
Hope this helps! Good luck with your training
