Vendetta - I too am a nervous passenger. I also suffer from circulation issues and find sitting for too long extremely uncomfortable (who doesn't?
). I need to walk around the cabin regularly, and when possible stand next to/behind my seat to watch movies etc. However, I do this because I really have to, and the moment I'm back in my seat that belt gets locked tight! BelArgUSA said to keep the time to a minimum, not that you shouldn't get up.
And remember there are excercises you can do in your seat to help improve your circulation.