Longest flight I have ever taken was from LAX to Melbourne, about 15 1/2 hours. After 10 - 12 hours your legs start aching and people had to stand up and march around the cabin to restore the blood flow. A 747-400 is a big plane.
ORD to Narita.
16 hours.
In coach.
Japanese passengers did not stop talking the entire time.
Still could smoke in the aft galley on JAL back then.
I did 14 hours, Hong Kong to Chicago. Thankfully I was in business class with direct aisle access.
I did fly from London to Johannesburg in economy, 10:36. Bloody awful.
I took that same flight in June 2007 with my daughter then aged 3 months. I survived. But yes, my feet were puffy once we landed
In the last few years I've done about a dozen or so 14-16 hour long flights...JFK-HKG,LA-SYD,Dubai-JFK.My cardiologist has strongly advised me to spend no more than an hour sitting without walking around for 15 minutes or more.I usually spend a lot of time standing in the rear galley...trying to get lucky(only kidding about "lucky").