My wife and I just came back from Europe. On the way over and back I got up 3 times to stand, streched my legs and walked around a bit. I even did knee bends. This was to avoid the the situation that I had read about of developing blood clots in your legs. All went well and seemed just fine.
Ten days after returning, I started to have a sharp jabbing pain in my right side below the arm pit. A half deep breath really hurt! I thought perhaps this was gas pain so I took some anti-gas pills when I got home from work which did not seem to help. The next morning I called the doctor and went in for an exam. He found nothing that looked suspicious and also ordered some chest x-rays. He was especially interested in my having had long flights recently. The next day at work he called and said the x-ray techician had spotted what might be fluid in my lungs. I was told to go to hospital and get a cat scan. The scan detected 7 clots in my lungs. Evidently, the pain I felt was the clots from my legs working their way up and in. I then got to spend 3 days in the hospital on a blood thinner IV and am now taking Warfin (a blood thinner) every day for the next 6 months.
The doctor said I did everything right to prevent the clots and this works 95% of the time. Someone makes up the 5% and unfortunately I was part of the 5%. He said perhaps taking a couple aspirin the day before and day of the flights would of lessened the chance of this happening? The point of all of this is to tell you that those nasty little clots are a real danger, they could of caused something "life altering" to have occured. I suggest that maybe you consult with your doctor a couple weeks before you fly to see what he/she might recommend to prevent this from happening to you, especially if you are over 50. I am 55. I might also say I have flown across the pond 3 time prior to this with no known problem.