In the past I was able to stand much of flights or get up frequently but now it seems the airlines desire more control over how much people are up and about so even tho I know you will look and act the spiney part due to pain maybe you'd want to wear a brace or something on the outside just to reinforce the appearance of needing to get up (if you've much trouble sitting en route).
Wishing you a very comfortable flight and all that follows
