If I take Benadryl (diphenhydramine) before getting on a plane, will the sedation from it help with my plane anxiety?

Causes drowsiness. Might suggest this be dealt with like one handles stage fright. Try a beta-blocker like propanalol or timolol. Another choice, alprazolam, which could keep you more awake. Talk to your doc, as these approaches are all generic and relatively cheap.