Airsickness?

Ok so, im flying to vegas on wednesday(5 hours). Im 17 and havent been on a plane since i was 10. I have a major case of emetephobia (fear of vomiting) While i have never gotten sick on a plane, I am scared that I will. I sometimes feel queasy when im in a car for too long, but i've never gotten sick. What are the odds of me getting airsick? What can I do for it? Drammamine sp? makes me sick which is weird. Can i take benadryl? Where is the best place to sit? Please help!