The better shape you are in the less you will feel the effects of aerobatics. Airsickness is the most common problem with novice pilots. The good news is that almost everyone has this problem and it goes away in time. I find being well rested and watching what I eat before a flight helps. A well rested body is also more suited for withstanding the increased G forces that occur in aerobatic flying.
Aerobatic competition is one of the most rewarding things a pilot can do.
Trying to stay in the box is the first challenge. The box is an imaginary cube in the sky that you must remain in while being judged.