You mentioned the long term sitting... and that is more of a problem than most ppl are aware of... get up more often and move around... don't sit with feet cross (or legs) sit on a pillow or cushion, raise your feet up while sitting

another thing is salt intake. If because it's hot you are drinking differently (drinks) check what you're drinking... and another thought, are you eating different foods that contain more salt than you are used to (canned foods, snack foods etc?)

Last year when I went to Disneyworld, I had a tropical drink from a kiosk near Italy... by the time I was at "Germany" my feet and ankles had swollen. This had never happened before (nor since) even though I always rent the motor chair. It had to be the drink.

TC! Think...you'll figure it out