I did go to the hospital ER, and a very nice, almost completely empty, clean and efficient place it was. All the (very young!) doctors and nurses looked terribly professional in their white t-shirts and white trousers, and all had mobiles which buzzed constantly to get them to attend to the next patient, deliver results etc. The nice young doctor tested my blood pressure and took a bunch of blood for blood tests (he was not a very skilled phlebotomist), and then the senior doctor showed up, he'd been called from home and was in jeans and a checked shirt. He patted my stomach in an affectionate way, checked to see if I had any pain anywhere, felt the level of swelling in my legs, and suggested this was just normal pregnancy swelling, particularly at a higher altitude, rather than anything more serious.
Once they got the blood tests back they confirmed I don't have pre-eclampsia, and although I didn't specifically get them to check for a DVT, they didn't mention it as a possibility. My blood pressure is 130/80 which is up from last measurement, but only by 10 points on each, and they weren't worried. My legs are not overly swollen, just a bit uncomfortable. All blood tests were fine, no liver enzyme problems, no infection, no elevated electolytes, blood clotting rate was spot on normal. The only minor issue was slightly low blood sugar so I was told to eat more regularly. Better than the other way round, at least. So they discharged me, with instructions to come back if I felt ill in any way.
Re DVTs I should point out that I do wear flight socks now on all flights, rather than just long haul. Previously I wasn't bothering on short flights, until I got swollen feet on a 45 minute flight from Paris about 6 weeks ago. I'm also still on baby aspirin which should lower the risk.
So thank you so much for your concern. I probably would not have gone to the hospital without your suggestions, and I'm really glad they checked me out. Thank you again. And remind me not to put on sandals with elastic that crosses over the feet. Not a good idea if feet are swollen!