Elizabeth
Dear Elizabeth: I highly recommend you seek out a doctor to learn more about potential prescription options or exercises that help treat anxiety before heeding my advice, but since you asked...
Edibles are the obvious choice for anyone looking to medicate or get high on the airplane. They can last most of the flight if you time it right (best to ingest a little over an hour before boarding, but start earlier if you have heavy anxiety during takeoff), and are easy (albeit illegal) to stow in your luggage.

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