And on the subject of DVT, over the summer warnings were issued (again) about frequent fliers suffering from it. It seems that those 'days' don't have to be continuous, or even consecutive. The recommendation of the airlines is that you get up and walk around for about five minutes every hour while on a flight. People who fly only a couple of times a year are at very low risk, even on long flights, but frequent fliers have an 'elevated' risk, based on length and frequency of flights, even though they spend days walking around in between.