There are varying strengths of tranquilisers - you might consider a small dose to take the edge off things and escalate your dose if you're struggling to manage the stress. Also betablockers have been an option for me in the past. Talk to your Dr about best available options and stress management while travelling.

Personally, I like the aisle so I can access the toilet. I also like the idea of seeing what the FAs are up to, as said upthread, there is no need to panic unless you see them panic. Seriously.

Have lots of peaceful entertainment - I would suggest a slasher flick on an iPad won't do much for your stress levels.

Don't hesitate to ask questions of the FAs, the ground crew, check in desk, basically any airline personnel. They are used to helping nervous flyers.

Wear comfortable clothes, you will find the trip more stressful if you're uncomfortable. Bring whatever travel aids you might want to improve your comfort levels, I like noise cancelling earphones as the noise of the engines can be draining for me. I've never taken a pillow purely cos I can't be bothered to carry one but I can understand those who do.

Stay hydrated. Eat before your travel and/or on long layovers. The food on the ground will be better than that in the air.

Otherwise, just try to relax and enjoy yourself.