9-hour flight. ankle was noticeably swollen. looks much better after 2 days. now thigh has bulging spot. mild aching. no redness or warmth. doctor?

Deep vein thrombosis: This definitely needs evaluation, because what you describe is consistent with a 'DVT' or deep vein thrombosis. Since you were sitting still for 9 hours, the blood in your legs wasn't circulating well- and that means you could have formed a clot in the leg that is swollen. A doctor can do a quick ultrasound to determine if that's true. Then, you may well need treatment depending on the findings.