I strongly prefer window seats, but once found myself in an aisle seat for a TransAtlantic flight. As I sat down, the man in the middle seat said "excuse me, but my son [gesturing to the window seat] is extremely claustrophobic. Is there any way you could change seats with him just for takeoff?" I couldn't believe my luck. I WANTED that window seat!
We changed places for the duration, and during the times when you aren't allowed to get up, he could at least lean out into the aisle and not have a seatback right in front of his face. He also got up and paced a lot. At the end of the flight, they thanked me again (which was crazy, so I thanked them) and apparently it had been a pretty unpleasant 8 hours, but he had got through it.
So do try to get an aisle seat. It made a big difference for him. If you end up in something else, ask those around you if you can trade and explain why. (I understand some people prefer aisle to window and might not trade, but you might luck out and meet me, or someone generous enough to trade even though they prefer the aisle.) Ask the flight crew if they can find you an aisle seat or arrange a trade with someone further away. And try to choose a flight at a time when you can sleep - nobody actually enjoys sitting on airplanes so if you can be asleep for some of it, so much the better.