I took a 14-hour flight and the woman at the window seat didn’t get up once. Selfishly, I was glad I didn’t have to move for her, but it’s dangerous to stay still at 35,000 feet. You need to keep your blood circulating by doing calf lifts or getting up.
Another way to help circulation is by wearing compression socks or tights, like those from Vim & Vigr. Yes, they can be difficult to get on, and I almost sprained an ankle trying to wiggle into tights in a airplane bathroom. They also help fight achy or tired legs.