I have traveled by airplane so many times now with rsd. It is a long and draining day but I will share some things that have helped me. I get a wheel chair to and from the gate. They will drop you off even just near if you want to get something to eat. Pre board and wait to get off till everyone else does. People may knock you or even step on you otherwise. If you can get a seat with the extra leg room that is good. Bring extra sweater. You know next time too I travel I am going to get a small blanket to place over my legs. The last flight I took from FL to CA was so cold a man let me use his jacket for my legs. Now I am not a fan of using strangers things cause of germs but my legs were in so much pain from the cold it was the lesser of two evils. Get up and walk around during the flight. Just go to the bathroom even. Plenty of water. I used to get an aisle seat but last time got a window and I think I liked that better. If you get a window and need to use the restroom tell a person you have a bad leg and can't climb over them. You know how some don't want to get up.
You will be fine. The anxiety of getting through the day is hard but you will do it. Bring some magazines,sometimes they have wifi,or tvs.