Hmmm...I can see that this one is going to run and run...
TG - if I may correct you without weakening your case, bed is a bad place to be as far as DVTs are concerned - otherwise spot on (tho' clambering out of your economy seat for a stroll can be a major excursion and is not exactly encouraged by cabin crew).
My better 'alf rather sourly comments that you are so bl**dy uncomfortable most of the time that you can't help fidgeting and giving your legs some exercise...
And on that note....