I do a few things.
1) I pay for extra leg room seats (but not exit row because I am not capable of opening the door myself). I have long limbs and I am more likely to hurt myself if I can't move my legs around a little.

2) I have a contoured memory foam travel pillow (like this type https://www.amazon.com/Traveling-Upgraded-Airplane-Headrest-Accessories/dp/B07SRRQS5B) but I wear it backwards so my chin rests in the dip. If I can swing a window seat I do and I rest my head against the wall.

3) headphones/earbuds to stream something I have seen or heard a million times for the noise but without it being distracting. I do not have recommendations for any headphones as I wear hearing aids that I can stream directly to. But any noise cancelling ones should be fine.

4) no fluids aside from water or gatorade for me. I can't have anything bubbly on a plane or I burp a lot and I can't relax.

5) Eye mask. It is never dark enough for me so I wear an eye mask like I would at home.

6) Wear layers. Sometimes flights are too hot, sometimes too cold. My plane outfit 100% of the time are compression leggings (not medical compression, workout compression), a super soft slightly oversized t-shirt, cardigan or sweater hoodie, slip on broken in sneakers, blanket scarf. I can easily take off the hoodie if I'm warm or if I'm cold I can use the blanket scarf as an extra layer draped over me.

I know a lot of those don't sound like pain relieving tips, but everything is designed to make me more comfortable in general and the less stressed and more comfortable I am the less likely I will be to contort myself into uncomfortable positions.